The death of a young Chinese migrant worker in Beijing has sparked an online protest by those sceptical of official claims that she committed suicide.

Highlighting suspicion of the government by Chinese society, hundreds of people have made online "anti-suicide" pledges to mock the police ruling that the woman killed herself.

"Hereby I say I won't commit suicide under any circumstances, for the Communist Party, for the country or for the people," said one using the name PY-Liu in a posting on a microblog.

"If I commit suicide, then it's definitely fake."

The government keeps a tight grip on the Internet, censoring content it deems politically sensitive or pornographic, but experts say the number and speed of microblog postings makes them more difficult to control.

Online postings had claimed the 22-year-old woman from the eastern province of Anhui was gang-raped and thrown to her death from the building of a clothing market in the May 3 incident.

But police say she jumped from the building and their initial investigations ruled out sexual assault and murder. Authorities have arrested a woman for "spreading rumours" about the case, state media have reported.

Another microblog user, yesir1, urged more to support the cause: "One wave after another! Microblogs are full of anti-suicide pledges. There has never been such a strange state of affairs in 5,000 years (of Chinese history)."

The case also sparked a rare public protest outside the clothing market in the tightly-policed Chinese capital on Wednesday, according to witnesses and Internet postings.

Participants reportedly included her relatives and other migrant workers but media reports, which could not be verified, said the family has accepted compensation of 400,000 yuan ($64,000) for her death.

The Jingwen market, a maze of hundreds of tiny clothing stores, is largely staffed by women who have moved to Beijing in search of jobs.

The case has now generated more than 35,000 postings online, many calling for greater transparency by authorities over the case.

"The police say the Anhui girl falling was a suicide without any violation (of her). There is serious doubt. Why not release all the surveillance videos?" said Fubai De Shehui.