Updated at 7:58 a.m. ET: CAIRO -- Egyptian police battled thousands of protesters outside President Mohammed Morsi's palace in Cairo on Tuesday, prompting the Islamist leader to leave the building, presidency sources said.

Officers fired tear gas at up to 10,000 demonstrators angered by Morsi's drive to hold a referendum on a new constitution on December 15. The Associated Press reported that some protesters broke through barbed wire around the building and hurled chairs and rocks at retreating police on Tuesday night.

The crowds had gathered in what organizers had dubbed "last warning" protests against Morsi, who infuriated opponents with a November 22 decree that expanded his powers. "The people want the downfall of the regime," the demonstrators chanted.

"The president left the palace," a presidential source, who declined to be named, told Reuters. A security source at the presidency also said the president had departed.

Morsi returned to work at the presidential palace on Wednesday morning, an aide later told Reuters.

The Muslim Brotherhood also called for a rally backing Morsi outside the palace on Wednesday and leftists planned a counter-demonstration, raising fears of clashes in a crisis over a disputed push for a new constitution. 

Morsi ignited a storm of unrest in his bid to prevent a judiciary still packed with appointees of ousted predecessor Hosni Mubarak from derailing a troubled political transition.

/

Egyptian protesters chant slogans against the Muslim Brotherhood during a rally in front of the presidential palace in Cairo on Tuesday.

Facing the gravest crisis of his six-month-old tenure, the Islamist president has shown no sign of buckling under pressure.

On Tuesday, riot police at the palace faced off against activists chanting "leave, leave" and holding Egyptian flags with "no to the constitution" written on them. Protesters had assembled near mosques in northern Cairo before marching toward the palace.

Supporters of Islamist president push Egypt to tipping point

"Our marches are against tyranny and the void constitutional decree and we won't retract our position until our demands are met," said Hussein Abdel Ghany, a spokesman for an opposition coalition of liberal, leftist and other disparate factions.

Protesters later surrounded the palace, with some climbing on gates at the rear to look down into the gardens.

At one point, people clambered onto a police armored vehicle and waved flags, while riot police huddled nearby.

The Health Ministry said 18 people had been injured in clashes next to the palace, according to the state news agency. 

Civil disobedience
Despite the latest protests, there has been only a limited response to opposition calls for a mass campaign of civil disobedience in the Arab world's most populous country and cultural hub, where many people yearn for a return to stability.

A few hundred protesters gathered earlier near Morsi's house in a suburb east of Cairo, chanting slogans against his decree and against the Muslim Brotherhood, from which the president emerged to win a free election in June. Police closed the road to stop them from coming any closer, a security official said.

Opposition groups have accused Morsi of making a dictatorial power grab to push through a constitution drafted by an assembly dominated by his supporters, with a referendum planned for December 15.

Liberals, Christians left out as Islamists back Egypt's draft constitution

They say the draft constitution does not reflect the interests of Egypt's liberals and other groups, an accusation dismissed by Islamists who insist it is a balanced document.

Egypt's most widely-read independent newspapers did not publish on Tuesday in protest at Morsi's "dictatorship". Banks closed early to let staff go home safely in case of trouble.

Abdelrahman Mansour in Cairo's Tahrir Square, the cradle of the anti-Mubarak revolt, said: "The presidency believes the opposition is too weak and toothless. Today is the day we show them the opposition is a force to be reckoned with."

Analysis: Crisis tests Egyptians' constitution

But after winning post-Mubarak elections and pushing the Egyptian military out of the political driving seat it held for decades, the Islamists sense their moment has come to shape the future of Egypt, a longtime U.S. ally whose 1979 peace treaty with Israel is a cornerstone of Washington's Middle East policy.

The Muslim Brotherhood and its allies, who staged a huge pro-Morsi rally in Cairo on Saturday, are confident enough members of the judiciary will be available to oversee the mid-December referendum, despite calls by some judges for a boycott.

"The crisis we have suffered for two weeks is on its way to an end, and very soon, God willing," Saad al-Katatni, leader of the Brotherhood's Freedom and Justice Party, told Reuters in an interview on Tuesday.

Reuters and The Associated Press contributed to this report.

More world stories from NBC News:

• Supporters of Islamist president push Egypt to tipping point
• North Korea pays tribute to Kim Jong Il's 'threadbare' parka
• ANALYSIS: Egyptians warn Morsi is no friend of US
• Bread and expired milk: School lunch scandal sparks outrage in China
• PhotoBlog: Building South Sudan from scratch
• ANALYSIS: UN Palestinian vote a personal victory for Abbas
• Fast cars go cheap as bubble bursts in 'China's Dubai'
• Experts: Antarctica, Greenland ice melting into sea

Follow World News from NBCNews.com on Twitter and Facebook

Ahmad Hammad / AP

A demonstrator chants slogans as several thousand supporters of President Mohammed Morsi surround the Supreme Constitutional Court on Sunday.

News analysis

CAIRO - There’s usually a lot of movement around Cairo’s highest court, and Monday was no exception. But acutely missing were the judges and lawyers themselves -- they’re on strike, protesting against the hundreds of Islamist demonstrators occupying the court’s grounds since Saturday night.

The judges -- seen by Islamists as holdovers from the regime of ousted President Hosni Mubarak -- have said they feel too intimidated to come and do their work, which would have included ruling on the legality of a 234-article draft constitution the opposition maintains is flawed, incomplete and above all else, leans too far toward Islamic law.

The scene was festive when NBC News visited the court. Small bands of men, many of them bearded, said they had come to support President Mohammed Morsi. They carried banners or posters and danced to pro-Morsi chants belted out through loudspeakers. Some sat reading newspapers or the Quran, or slept on the shaded grass around the imposing stone building. Fresh replacements were bused in every morning, participants told NBC News.

Crisis tests Egyptians' constitution

The phalanx of riot police -- around 100 in all -- formed a cordon around the protesters, not the courthouse. Instead of protecting judges and allowing them to get into the courthouse, they appeared to be protecting the protesters. 

Protester Waheed Amr laughed as he held up his ID card showing he was a member of the judiciary police.

"The police are here to protect the judges, not us. We can protect ourselves," he said.  

Amr just laughed again when a reporter pointed out that there were no judges to protect.

"We support the revolutionary decisions of our president," he said. "He's cleaning up the country, and we are here to deliver a message of support."

In revolution, he seemed to say, physicality can trump the rule of law, because it becomes the law.

The pro-Morsi sit-in at the high court is a counter-point to the 11-day camp-out in Tahrir Square, the symbolic heart of the broad-based revolution that overthrew Mubarak in 2011. Over there, several hundred die-hard opponents chant against Morsi’s controversial decrees and his support for what many see as an openly pro-Islamist constitution. 

NBC News

"We support the revolutionary decisions of our president," protester Waheed Amr said outside of Egypt's highest court. "He's cleaning up the country, and we are here to deliver a message of support."

And the high court sit-in only complicates efforts as the hodgepodge of liberal, secular, moderate and Christian minorities ponders what to do next.

In 12 days it looks likely that a national referendum on the draft constitution will take place. On Monday, Morsi’s top legal adviser said that preparations were already under way. And, after hundreds of judges from a union called the Judges Club announced that its members would not oversee the running of the polling stations, the powerful Supreme Judicial Council -- a body comprising thousands of judges -- agreed to oversee the Dec. 15 referendum.  

So far, Morsi's opposition looks out-maneuvered.

Liberals, Christians left out as Islamists back Egypt's draft constitution

Meanwhile, the opposition’s options are between two rocks and a hard place: it either boycotts the constitutional referendum, effectively ending its campaign for power and influence; or it fights hard to win a "no" vote and loses, which weakens it but strengthens Morsi by legitimizing the current draft; or it surprises everyone and wins a "no" vote, which would only move the whole process back to square one and give the president another five or six months of special powers to hand-pick yet another group to write a draft constitution.

The anti-Morsi judges also have their backs to the wall. Even if they find the nerve to meet at the high court or somewhere else and dissolve the body that wrote the draft constitution -- they could chose to do so because it was created under questionable laws -- their ruling would have no legal effect, as Morsi’s recent decrees give him and the writing body immunity from judicial review.

So until there’s a new constitution, Morsi holds all cards -- executive, legislative, and now, judicial.

But, if that’s the case, why are pro-Morsi protesters preventing Egyptian judges from doing their job in their own courtroom? "Look," said Amr, "the gates of the court are open! We’re not cutting off the courthouse. We’re here to tell the court to stay out of politics!"

In doing so with brute force and intimidation, have Morsi and his supporters reached what some Middle East analysts are calling a tipping point in the two-year old revolution? One that now looks increasingly like it's sliding toward an Islamic state?

Jim Maceda is an NBC News foreign correspondent based in London who is currently on assignment in Cairo. He has covered the Middle East since the 1970s.

More world stories from NBC News:

• North Korea pays tribute to Kim Jong Il's 'threadbare' parka
• ANALYSIS: Egyptians warn Morsi is no friend of US
• Bread and expired milk: School lunch scandal sparks outrage in China
• PhotoBlog: Building South Sudan from scratch
• ANALYSIS: UN Palestinian vote a personal victory for Abbas
• Fast cars go cheap as bubble bursts in 'China's Dubai'
• Experts: Antarctica, Greenland ice melting into sea

Follow World News from NBCNews.com on Twitter and Facebook