Founder of human rights website and three others are held after reporting incidents including apparent self-immolation in Beijing

Chinese authorities have detained the director of a human rights website and three citizen journalists, one of them 17 years old, for reporting two recent "incidents" in Tiananmen Square, including an apparent self-immolation.

Police detained Huang Qi, the founder of the rights website 64 Tianwang, at about 3pm on Thursday in the south-western metropolis Chengdu, his mother Pu Wenqing said in a phone interview. Tianwang had posted many of the detained journalists' reports.

"Seven police officers came directly to our home, some of them Beijing police," Pu said. "They said they wanted to understand a situation," without giving further details. The officers confiscated Huang's computer, mobile phone and USB thumb drives, she said. Huang is being held incommunicado at a local police station.

Police detained the Tianwang volunteer Wang Jing on Friday and sent her back to her home province Jilin, where she remains in criminal detention on charges of "provoking and stirring trouble", the website reported. They arrested two more volunteers, Liu Xuehong and Xing Jian, 17, on Saturday morning.

Wang reported the apparent self-immolation attempt on 5 March, the first day of the National People's Congress, an important political conclave in Beijing that ended on Thursday. Pictures posted online show smoke clouds rising from a distant spot near the Forbidden City, which abuts the enormous flagstone square. Little else is known about the incident.

"There was smoke coming from near the Jinshui bridge, and I ran over to see what was happening," Wang told the broadcaster Radio Free Asia. "I saw white stuff [extinguisher foam] everywhere; you couldn't see the person, and then they started to clear the area and the police wouldn't let people take photos."

One day later, Xing reported that a 30-year-old man had vandalised the giant portrait of Mao Zedong that overlooks the square by pouring ink on its lower left-hand corner. Police quickly whisked the man away and blocked off a 200-metre area around the site.

"Journalism is not a crime and these three activists should be released immediately," William Nee, China researcher at Amnesty International, said in a statement. "Their detention shows the disturbing lengths the authorities are willing to go to control the message during the National People's Congress."

The three volunteers had gone to the square to report on petitioners, disgruntled citizens who travel to Beijing from afar to air their grievances to higher authorities.

Huang has been arrested many times for his activism. In September, police held him for questioning overnight after he protested in support of Bo Xilai, a fallen Communist party boss serving a life sentence for corruption, embezzlement and abuse of power.