China has detained at least four people including the founder of a citizen-run news website which reported that a woman set herself on fire last week in Beijing's Tiananmen Square, a rights group said Thursday.

Huang Qi, founder of 64TianWang, a website which compiles reports from volunteers across China, was "taken away by 11 police officers", on Thursday in the southwestern city of Chengdu, London-based advocacy group Amnesty International said.

In a series of raids in the past week, police also detained at least three citizen journalists who contribute to the website -- Liu Xuehong, Xing Jian and Wang Jing -- all on charges of "picking quarrels and provoking troubles", Amnesty added in a statement.

Citing witnesses, at least two of those said to be detained had told foreign media that a woman had attempted to self-immolate last week in Tiananmen Square, the symbolic centre of the Chinese state. The 64TianWang website published photos showing smoke in the area.

"There now appears to be a concerted campaign of intimidation by the Chinese authorities against those associated with the 64 Tianwang website," said William Nee, China researcher at Amnesty International.

"Once again the authorities have shown their intent to stifle debate on human rights within China."

Amnesty's report comes at a time when China's ruling Communist party is seen as increasingly curbing dissent and stepping up controls on online speech as well as domestic media.

Police did not comment on the 64TianWang report, but state media later said that an "emergency" had occurred in Tiananmen Square at roughly the same time as the alleged immolation attempt.

The People's Public Security News report gave few details but said that the incident occurred in the "Tiananmen area" as Chinese Premier Li Keqiang was delivering a high-profile speech to senior officials including President Xi Jinping in a building which flanks Tiananmen Square.

Later that day China's vice-minister of public security presented two police officers with awards for dealing with the incident, the report said, without giving any further details.

Tiananmen Square is always subject to strict control, with many security personnel equipped with fire extinguishers, apparently in an attempt to prevent protests by disgruntled citizens.

There have been more than 120 attempted self-immolations by Tibetans protesting against Chinese rule since 2009, most of them fatal.

Chinese people resisting forced demolitions of their houses have occasionally resorted to setting themselves on fire.

Chinese police were not immediately available for comment. A mobile phone number recently used by Huang Qi could not be reached.