Hundreds of people protested outside a Beijing market building Wednesday, demanding an open investigation into the death of a migrant worker who plummeted from the building on Friday.

A large number of policemen, including armed forces and helicopters were sent onsite to dispel the crowd, while police said there was no evidence of foul play in the preliminary investigation, dismissing public speculation that the woman was gang raped and thrown out of the building.

Although mass incidents are becoming more frequent in China, such events in Beijing remain rare. The capital police pays close attention to maintaining social order and a protest on this scale has propelled the matter beyond an ordinary investigation.

Beijing police said the surveillance camera captured the woman, 22, surnamed Yuan, entering the building in the evening of May 2 alone, before falling to her death at 5 am the next day. She had no interaction with other people during her one-night stay, said police, and neither an on-site investigation nor a later autopsy suggested any signs of suspicious conditions.

A crowd gathered at the Jingwen Market in the capital's Fengtai district at around 10 am shouting slogans and holding banners, a nearby shopkeeper told the Global Times.

Witnesses said the protesters were mostly from Anhui Province, where the dead woman came from, and included her family and friends.

The gathering, which had attracted thousands of on-lookers by noon, was dismissed by police at around 2 to 3 pm, another witness told the Global Times.

A major street that had been blocked since the morning was reopened at 5 pm.

Rumors have been circulated online that Yuan was gang raped in a enclosed room inside the building by seven security guards, which led to her suicide, or that they even pushed her out. Yuan's mother visited the Dahongmen Police Station supervising the market but was not allowed to see the surveillance footage, some Web users said.

The case attracted wide attention online with Weibo users widely reposting the police's announcement.

One Web user posted a picture showing a dead body lying on the ground and claimed it was the scene of Yuan's death. However it turned out the photo was lifted from a Hong Kong TV show.

However, comments or re-posts were quickly removed off Weibo, and the Beijing Public Security Bureau closed comments for their post on the case.

As recent massive protests have triggered nationwide debates, including one against a chemical plant in Kunming, experts have suggested that the government needs better ways to maintain stability.

Xia Xueluan, a professor with the Institute of Sociology and Anthropology of Peking University, told the Global Times that a major reason for this nationwide attention is that it involves the vulnerable migrant worker community.

"If it's just a normal suicide, why can't I talk about it?" asked one Weibo user. "I demand the police release the surveillance video and let the public share their opinions freely."

Searching and commenting are not allowed because the authorities hope the discussion will gradually die down, Xia said, but added that controlling information would only arouse more anger and speculation from the public.

The bureau should release the information demanded by the public in the face of speculation, before its credibility is  ruined, said Xia.