Bobby Yip / Reuters

People take part in a candlelight vigil at Hong Kong's Victoria Park on Monday to commemorate those who died during the military crackdown of the pro-democracy movement at Beijing's Tiananmen Square on June 4, 1989.

BEIJING – Government controls many aspects of life in China, but for today at least the invisible hand of market forces proved too strong even for the country’s ruling Communist Party.

In an apparent coincidence, Shanghai’s local stock market, the Shanghai Composite Index, opened trading this morning at 2346.98 points. Read backwards, it looks like the date, June 4, 1989 – this day 23 years ago when the Communists brutally cracked down on pro-democracy activists in Tiananmen Square and elsewhere in the capital.

Even more bizarre? By the end of trading in the afternoon, the market had lost 64.89 points.

PhotoBlog: Thousands remember Tiananmen Square crackdown

The significance of the numbers might have passed without comment had authorities not tried to censor discussion of the anniversary by preventing users on Weibo - China’s equivalent of Twitter – from posting terms such as “six four,” “candle” and “never forget.” With users abuzz over the Shanghai Composite Index numbers, censors had to widen the list of banned terms to include the Chinese word for ‘Index’.

Hundreds of students and other civilians are estimated to have been killed in 1989 as People’s Liberation Army soldiers entered the capital to clear the streets of protesters. The topic of the crackdown is taboo in this country and little discussed aside from sanitized official accounts in textbooks that call the event a “political disturbance.”  

Security around Tiananmen Square is typically boosted before the anniversary and censors work to keep discussion to a minimum. 

State Department deputy spokesman, Mark Toner, issued a statement on Sunday urging the Chinese government to "release all those still serving sentences for their participation in the demonstrations; to provide a full public accounting of those killed, detained or missing; and to end the continued harassment of demonstration participants and their families."

In response, Chinese Foreign Ministry spokesman, Liu Weimin, called U.S. statements on the June 4th incident a “crude meddling in domestic Chinese affairs.”

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Andrew Kelly / Reuters

Protesters lay in front of a mock tank as part of a demonstration in New York on Sunday to mark the 23rd anniversary of the The Tiananmen Square protest in China.

The United States urged China to free all those still jailed over the 1989 Tiananmen Square pro-democracy demonstrations on the 23rd anniversary of the brutal crackdown.

State Department deputy spokesman Mark Toner issued a statement late on Sunday calling on the Chinese government on Sunday "to provide a full public accounting of those killed, detained or missing."

The statement said the U.S. "joins the international community in remembering the tragic loss of innocent lives" -- a comment unlikely to be welcomed by China’s ruling Communist Party.

Hundreds, perhaps thousands, are believed to have died when the government sent in tanks and soldiers to clear Tiananmen Square on the night of June 3-4, 1989, violently crushing six weeks of protests.

Regaining moral high ground? Google tells Chinese when they're being censored

More than two decades later, Beijing still considers the incident a "counter revolutionary rebellion" and has refused to acknowledge any wrongdoing or consider compensation for those killed, The Australian newspaper reported.

Meanwhile, China censors blocked internet access to the terms "six four," "23," "candle" and "never forget" on Monday, broadening extensive efforts to silence talk about the anniversary.

Searches for the terms related to the anniversary, such as "six four" for June 4, were blocked on Sina Weibo, the most popular of China's Twitter-like microblogging platforms. Users encountered a message that said the search results could not be displayed "due to relevant laws, regulations and policies."

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"It's that day again and once more numerous posts are being deleted," a Sina microblogger wrote. Sina was not immediately available for comment.

China's censors also blocked access to the term "Shanghai stock market" on microblogs after the index fell a bizarre 64.89 points on the anniversary.

PhotoBlog: Thousands remember Tiananmen Square crackdown

In another twist, the Shanghai Composite Index opened at 2346.98 points on the 23rd anniversary of the killings in either a deft piece of manipulation or an uncanny double coincidence. The numbers 46.98 are June 4, 1989, backwards.

"Whoa, these figures are too freaky! Very cool!" said a microblogger. "The opening figure and the drop are both too creepy," said another. 

For more coverage of China, see Behind The Wall

The anniversary of the date on which troops shot their way into central Beijing in 1989 has never been publicly marked in mainland China.

The government has never released a death toll of the crackdown, but estimates from human rights groups and witnesses range from several hundred to several thousand.

Yao Jianfu, author of a new book of interviews with Chen Xitong, the Beijing mayor at the time of the crackdown, told Reuters that Chen had said "this was a tragedy that should have been averted but wasn't".

"I never foresaw there would be shooting, because Mao Zedong said that ordinary people should not be shot at and suppressing student protests comes to no good," said Yao.

The government has restricted the movements of dozens of dissidents, former prisoners and petitioners during the anniversary period and warned them against speaking to journalists or organizing activities, said Songlian Wang of rights group Chinese Human Rights Defenders.

A coalition of lawyers and rights activists began a one-day fast in their homes on Monday to commemorate the anniversary, said a Shandong-based lawyer, Liu Weiguo.

Tens of thousands of people are expected to attend a candlelight vigil in Hong Kong, said organizers, who had erected a replica of the Goddess of Democracy that was built in Tiananmen Square in 1989.

Chinese tourists stopped on Tiananmen Square shook their heads and appeared mystified when asked about the anniversary. There were no obvious signs of extra security on the already well-guarded square.

But a trinket vendor said he was well aware what day it was.  "Do foreigners also know about June 4?" he asked a Reuters reporter in a hushed tone, looking around to make sure nobody heard him. "I think it is important we remember but nobody will talk about it now." 

Reuters and msnbc.com's Alastair Jamieson contributed to this report.

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