Hundreds of ordinary Chinese with complaints against the government are being held in an unofficial detention center near Beijing as the nation's leaders conclude a top-level meeting.
Petitioners held in the Jiujingzhuang detention center since Monday evening said on Tuesday that unidentified men had beaten some of them.
"Early this morning at 3:00 a.m. a policeman, some private security guards, and four or five hired thugs came in and tried to drag some of us out," said Huangshan-based petitioner Zhang Meijuan.
"We refused to go with them, because they didn't show any identification, and we didn't know who they were," Zhang said.
"They beat us up," she said, adding that there were at least 200 petitioners still being held in the center. "They only left when everyone piled in against them."
She said four petitioners had sustained "various levels of injuries."
Fellow petitioner Wu Changzhong said he had suffered leg injuries in the attack. "They pulled a whole bunch of my hair out, and one of my legs is injured and I can't move my arm," he said.
"These were thugs hired by the government," he said of his attackers. "They pulled us out and attacked us in the middle of the night."
Petitioner and detainee Wang Jingfeng said he had taken note of the policeman's registration number. "The people who actually attacked me were criminal gang members from Beijing," he added.
The attack came as China's ruling Communist Party wrapped up a top-level annual leadership meeting in Beijing.
Beijing police typically crack down on petitioners and rights activists around important political events and anniversaries.
China's ruling Communist Party leaders are meeting in Beijing to debate "cultural reforms," which some interpret as a tightening of control over media and the Internet, ahead of a leadership succession scheduled for next year.
Thousands of ordinary Chinese with complaints against the government have converged on the capital during the holiday period and ahead of the Central Committee plenum, and police have stepped up operations to detain them.
The Party is gearing up for a power succession one year from now, when new leadership will be chosen following the resignation of President Hu Jintao as Party general secretary.
President Hu, his premier Wen Jiabao, and the powerful Standing Committee will then relinquish all remaining leadership posts in 2013, with vice-president Xi Jinping widely tipped as Hu's successor.
Shanghai-based petitioner Mao Hengfeng said on Monday that around 2,000 petitioners were being held at Jiujingzhuang, with room only for standing.
The number of ordinary Chinese traveling to Beijing to pursue grievances against the government typically swells ahead of key political dates, as petitioners hope their cases will get a more sympathetic hearing.
Reported by Qiao Long for RFA's Mandarin service. Translated and written in English by Luisetta Mudie.