Zhao has campaigned relentlessly for parents whose children suffered from drinking milk tainted with the melamine chemical, which killed six children and sickened nearly 300,000 others in a scandal that erupted in September 2008.

Qi Zhiyong, a dissident who lost a leg during the crackdown on the 1989 Tiananmen democracy protests, said he had also been detained for trying to organise a human rights seminar on November 9 in a Beijing park.

In a text sent to AFP, Qi said he and fellow organisers had planned for the seminar to last until the end of Obama's visit.

He had also applied to police to protest the US President's visit, "to press him to pay attention to human rights in China, people's livelihoods and the relatives of jailed people, as he comes only to talk about climate change."

Qi said he was being held in the Beijing suburbs and had been charged with unlawful assembly and disturbing the social order.

He added that Li Jinping, who every year tries to organise commemorations of deposed former leader Zhao Ziyang, who opposed the use of force to quell the 1989 protests, had also been detained.

Yang Qiuyu, a housing rights activist, and more than 30 other petitioners had also been taken away, Qi said.