PRAGUE -- A powerful explosion badly damaged an office building in the center of the Czech capital Monday, injuring up to 40 people. Authorities believed people might still be buried in the rubble.

It was not certain what caused the blast in Divadelni Street, in Prague's Old Town, at about 10 a.m. local time (4 a.m. ET), but it was probably a natural gas explosion, police spokesman Tomas Hulan said. Tourists at the famed Charles Bridge also felt the blast.

The street was covered with rubble and was sealed off by police who also evacuated people from nearby buildings and closed a wide area around the explosion site.

Zdenek Schwarz, head of the rescue service in Prague, said up to 40 people were injured, at least four of them seriously.

David W Cerny / Reuters

An estimated 40 people were injured Monday when an explosion ripped through a building in Prague, the capital of the Czech Republic. Authorities say some people are feared to be buried in the rubble and that natural gas is suspected as the cause.

Rescue service spokeswoman Jirina Ernestova said there were foreigners among the injured but had no further details immediately.

Some of the injured were taken to Prague's hospitals for treatment while others, many of whom were hit by flying glass, were treated by rescuers at the scene.

Firefighters' spokeswoman Pavlina Adamcova said rescuers were still searching the rubble, using sniffer dogs.

Adamcova said two or three people were still missing.

Windows in buildings located hundreds of yards from the blast were shattered, including some in the nearby National Theater.

"There was glass everywhere and people shouting and crying," Vaclav Rokyta, a Czech student, told the AP near the scene.

"I was in the bathroom, no windows, the door was closed. Honestly, if I had been in my bed I would have been covered in glass," said Z.B. Haislip, a student from Raleigh, North Carolina, who was in a nearby building.

The Faculty of Social Sciences of Prague's Charles University and the Film and TV School of the Academy of Sciences of Performing Arts are located next to the damaged building.

The road closures caused major traffic disruption and confused thousands of tourists. Some new arrivals to the city had to stand on street corners, unable to reach their hotels, their baggage loaded onto trolleys. Hotel staff urged them to be patient.

Prime Minister Petr Necas said in a statement he was "deeply hit by the tragedy of the gas explosion."

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PhotoBlog: Rescuers help injured amid the rubble

This story was originally published on Mon Apr 29, 2013 7:54 AM EDT

David W. Cerny / Reuters

Demonstrators in Prague protest communist victories in regional government elections. In opinion polls, the Communist Party of Bohemia and Moravia (KSCM) has jumped past ruling conservative parties to second place.

PRAGUE -- Before the fall of communism, Vaclav Sloup trained the soldiers who caught thousands trying to flee across Czechoslovakia's fortified border to West Germany.

Today, he helps power a Czech Communist Party that has surged to second place in polls, tapping anger over poverty and graft.

When communism collapsed in 1989, the once-dominant party was slow to produce the same kind of reformist wing as emerged in other Eastern European countries. While statues of Lenin have vanished and the party insists it has reformed, its lawmakers still greet one another with "comrade" and maintain hard-line foreign policy views such as leaving NATO.

The Communist Party of Bohemia and Moravia remains a pariah to many, but it is a pariah commanding 20 percent of the vote.

Sloup's rise to become education councilor in the northern region of Karlovy Vary has aroused protests by students and former dissidents that demonstrate the strength of emotion, but the 63-year-old refuses to quit because of his past.

"I carried out my duties when Europe was divided by an Iron Curtain, and it was in accordance with laws of the time," he said. "I have nothing to be ashamed of." 

However, two Communist councilors, one a former border guard and secret police informant, resigned after demonstrations against the party in Bohemia.

"The Communist Party is anti-democratic," said David Pithart, a 47-year-old environmental consultant, whose father Petr was a leading dissident and served as Czech prime minister in 1990.

"The party doesn't know how to govern any other way," he said while at a protest in Ceske Budejovice in December. 

Second most popular party
The communists have jumped past ruling conservative parties to second place in polls and would be a prospective partner for the poll-leading, center-left Social Democrat Party after a 2014 general election.

Social Democrat leader Bohuslav Sobotka now talks openly about prospects of forming a minority government backed by communists. He wants to avoid a repeat of 2010, when his party won the most votes but could not find a partner that would allow it to form a government.

Any cooperation, however, would require ending a 1995 ban on government-level cooperation with the communists.

The Social Democrats will debate this controversial issue at a national congress March 15-16, and many delegates may yet shrink from any close political contact.

Should they refuse to deal with the communists, the country would most likely face an awkward coalition of left and right parties that could stall policymaking.

Easing the 1995 ban could shift Czech politics to the left, allowing a political consolidation and ending years of unstable rule in which cabinets with a shaky power base have repeatedly been unable to push through their full agenda.

Prime Minister Petr Necas, a center-right politician, has called the Communist Party "unreformable."

The communists' return has given rise to soul-searching for many beyond the ranks of party politics in the central European country of 10.5 million.

In October, the communists won spots on governing councils in the majority of the country's 13 regions in regional elections, gaining 20.4 percent of the overall vote versus 12.3 percent for Necas' Civic Democrats.

Sitting under a portrait of Karl Marx, Communist Party Deputy Chairman Jiri Dolejs said the party had apologized repeatedly for repressions of the communist era, but may yet need to make another gesture to link up with the Social Democrats.

"We are now the closest to a coalition in 23 years," he said from his office in the party's massive, nondescript headquarters, which sits on Political Prisoners Street.

For some, harsh aspects of communist rule have given way to rosier memories of a system that for all its darker aspects offered job security, cheap housing and low-cost food.

Those memories are growing stronger, especially among retirees and blue-collar workers, as the country suffers the longest recession of its post-communist history, having contracted since mid-2011 because of state spending cuts.

A January survey found that just 46 percent of people felt that today's system was better than communism, a 21-year low.

"After almost a quarter of a century, the (communist) stigmatization is not so strong anymore," said Dolejs, an economist who joined the communists in January 1989.

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Radek Mica / AFP - Getty Images

Left to right, Lech Walesa, Poland's president from 1990-1995, former U.S. chief diplomat Madeleine Albright and former U.S. president Bill Clinton, attend the funeral service for former Czech president Vaclav Havel at the St. Vitus Cathedral in Prague, on December 23, 2011. Havel, a dissident and playwright who was the hero of the 1989 Velvet Revolution against communist rule and became his country's first post-independence president, died on December 18, 2011 aged 75. World leaders joined Czech dignitaries to pay homage to Havel at his state funeral in the historic Prague cathedral.

Michael Sohn / AP

Mourners react as the car with the coffin passes during the state funeral of former Czech President Vaclav Havel in the St. Vitus Cathedral in Prague Friday, Dec. 23, 2011. Havel was the leader of the peaceful anti-communist "Velvet Revolution." He died Sunday, Dec. 18, at age 75.

AP reports:

Odd Andersen / AFP - Getty Images

Britain's former prime minister John Major and current prime minister David Cameron arrive for the funeral service for former Czech president Vaclav Havel in Prague, on December 23, 2011.

Czechs and world leaders paid emotional tribute to Vaclav Havel on Friday at a pomp-filled funeral ceremony, ending a week of public grief and nostalgia over the death of the dissident playwright who led the 1989 revolution that toppled four decades of communist rule.

Bells tolled from churches while a wailing siren brought the country to a standstill in a minute of silence for the nation's first democratically-elected president after the nonviolent "Velvet Revolution."

Havel's wife Dagmar, family members, friends and leaders from dozens of countries gathered Friday at the towering, gothic St. Vitus Cathedral which overlooks Prague. U.S. Secretary of State Hillary Rodham Clinton, French President Nicolas Sarkozy and Britain's Prime Minister David Cameron were among some 1,000 mourners who bowed their heads in front of the coffin draped in the Czech colors. Continue reading...

Milan Jaros / EPA

Scouts watch the funeral of late Former Czech President Vaclav Havel in the courtyard of the Prague Castle in Prague.

Petr David Josek / Pool via EPA

Soldiers carry the coffin during the state funeral of late former Czech President Vaclav Havel in the St. Vitus Cathedral in Prague.

David Brauchli / Getty Images

Mourners watch the state funeral of former Czech President Vaclav Havel transmitted live onto large-screen monitors outside St. Vitus Cathedral on December 23, 2011 in Prague, Czech Republic.

David W. Cerny / Reuters

A picture of the late former Czech President Vaclav Havel is seen among lit candles placed in tribute to him at Wenceslas Square in Prague December 22, 2011. Havel, an anti-Communist playwright who became Czech president and a worldwide symbol of peace and freedom after leading the bloodless "Velvet Revolution", died at the age of 75 on Sunday.

Petr Josek / Reuters

People gather to mourn as the coffin of former Czech President Vaclav Havel is transported on a gun carriage to Prague Castle for the funeral ceremony in Prague, Czech Republic, on Dec. 21, 2011.

Petr Josek / Reuters

A hearse transporting Havel's body to Prague Castle.

Reuters reports from PRAGUE:

Vaclav Havel's actress wife led mourners through the streets of Prague Wednesday, following the playwright-president's body on its last public journey, to the castle where it will lie in state until a funeral Friday.

Dagmar Havlova was joined by leading figures from the Czech state and society as well as thousands of the former dissident's fellow citizens wishing to pay tribute to the man who died on Sunday, 22 years after leading the "Velvet Revolution" that ended Communist rule over Czechoslovakia in December 1989.

"This was an honest man," said 67-year-old Jaroslava Leskakova as she marched in the somber cortege behind the hearse through the sunlit cobbled streets of the old city toward the landmark Charles Bridge that leads to Prague Castle.

"He did not think of himself but did all he could for people to be happy," said Leskakova of Havel.

Michal Kamaryt / AP

People jangle keys in a symbolic reference to the Velvet Revolution of 1989 as Vaclav Havel's body makes its final public journey.

Marko Drobnjakovic / AP

Dagmar Havlova, right, Havel's widow, and her daughter Nina Veskrnova, left, follow the vehicle carrying his coffin.

Vit Simanek / AP

Soldiers carry the coffin of former President Vaclav Havel as they reach Vladislav Hall at Prague Castle.

Havel was repeatedly jailed by the Soviet-allied Communist authorities in the 1970s and 80s for his activism in the Charter 77 civil rights movement and then led the nation as president from 1989 to 2003.

Moving from an arts center Havel helped found, where it had lain on view since Monday, to the castle he found himself suddenly thrust into as head of state, Wednesday's journey was symbolic of the transformation in Havel's own life, from censored playwright to a statesman rebuilding eastern Europe. Continue reading.

Related content:

• 'Velvet Revolution' icon Vaclav Havel dead at 75
• Slideshow: Year in review - Newsmaker farewells 2011

Petar Kujundzic / Reuters file

Presidential candidate Vaclav Havel waves to his supporters from a balcony in Prague in this Dec. 19, 1989 file photo. Havel, a dissident playwright who was jailed by Communists and then went on to lead the bloodless "Velvet Revolution" and become Czech president, died at 75 on Dec. 18, 2011.

From msnbc.com news services:

"Truth and love must prevail over lies and hatred," Havel famously said. It became his revolutionary motto which he said he always strove to live by.

Havel was nominated several times for the Nobel Peace Prize, and collected dozens of other accolades worldwide for his efforts as a global ambassador of conscience, defended the downtrodden from Darfur to Myanmar.

Among his many honors were Sweden's prestigious Olof Palme Prize and the Presidential Medal of Freedom, the highest U.S. civilian award, bestowed on him by President George W. Bush for being "one of liberty's great heroes."

An avowed peacenik whose heroes included rockers such as Frank Zappa, he never quite shed his flower-child past and often signed his name with a small heart as a flourish.

Read the full story here.

Petr David Josek / AP

People gather under a Czech national flag as thousands mark the passing of former Czech president Vaclav Havel at the Venceslaw's square in Prague, Czech Republic, Sunday, Dec. 18.