Among those the group paid tribute to was Ding Zhijian, 32, an editor at a publishing house who drowned in his car after it became trapped in three metres of water on Saturday last week.

The mourners also placed a board listing the 66 victims identified so far.

More people joined the crowd when a 27-year-old man put up a banner calling for officials to take responsibility for the deaths and publish details on how the disaster relief funds are being used.

Residents have been strongly critical of the official response to the disaster triggered by the worst rainstorm to hit the capital in more than 60 years, and of the four days it took officials to update their initial death toll of 37.

'Release all the names of people who were killed and who remain missing. Publicise the names of the people who should be held accountable and tell us the punishment they should receive,' the banner read.

The protester was quickly surrounded by journalists.

'I'm not a Beijing native, but I live in this city for work,' the man said. 'I'm scared, but I do not regret what I have done.'

Dozens of uniformed policemen began to break up the swelling crowd within a few minutes.

No force was used but several foreign cameramen were asked to show their credentials.

Several plain-clothes police officers took photographs of the crowd.

Police were well prepared for the gathering, which came in response to an online call posted on social media websites such as Sina Weibo. At least one police vehicle was parked at each junction of the Guangqumen bridge and nearby bridges on the second ring road, while a new surveillance camera was being installed under the bridge at around 1pm.

Zhou Ai , who lives near the bridge, said police followed her at the mourning.

'The local police warned me in the morning I shouldn't leave my apartment today,' she said.

Another activist, Hua Cuo , said his Sina Weibo microblog account had been censored by the police.

Additional reporting by Keith Zhai