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Ms. Wang had rented a bed — a wooden plank on bricks — in a tiny concrete room shared with two others. A gang of two dozen men barged in one night at 11 p.m., demanded to see her ID, searched her belongings and grabbed her cellphone.

“I was scared to death when they suddenly barged in here,” Ms. Wang said, pointing at the door, where the lock had just been replaced.

The men refused to identify themselves and bundled her into a minivan with other petitioners. At another stop, she saw a couple dragged into the vans in their pajamas, the woman wearing only one shoe.

All were taken to a police station in nearby Jiujingzhuang village, where many petitioners say police process them for return to their hometowns. Using someone else’s identity, Ms. Wang was able to evade police suspicion and was released. Many of the others were sent back, she said.

The raids are having an effect. The compound that houses her room and others now has only a handful of residents, down from about 30.

“They’ve all been chased away, caught or scared home,” said Liu Zhifa, a 67-year-old petitioner from Henan province and one of the holdouts. Mr. Liu confirmed Ms. Wang’s description of the Oct. 31 raid and described his own encounter with thugs breaking his lock and entering his room three times in one night in mid-October.

“I asked them to show their identifications, and they yelled at me, saying: ‘What right do you have to see our identification? Who do you think you are?’” Mr. Liu said. “They were ruthless. The authorities and the police are working with people in the underworld.”

A police officer who would only give his surname, Wei, answered the phone at a Jiujingzhuang police station (not ‘the’ because the police station has another name) and denied that authorities were raiding petitioners’ villages. “We only act according to the law,” Mr. Wei said. Questions about the broader crackdown were referred to the Beijing public security bureau, which did not respond to faxed questions.

The crackdown has extended to lawyers such as Xu Zhiyong. He said Beijing authorities have held him under informal house arrest since mid-October, stationing four or five guards outside his apartment in Beijing around the clock.

Mr. Xu has campaigned for years against Chinese authorities’ use of “black jails,” or unofficial detention centers run by local governments to hold petitioners. The government has denied the existence of such facilities, but even the tightly controlled state media have reported on them.

“The illegal restriction of a citizen’s personal freedom for a long period of time is criminal behavior,” Mr. Xu wrote in an email. “In an authoritarian state, this type of crime takes place everywhere.”

Authorities in Shanghai also have ratcheted up pressure on critics, sentencing veteran women’s rights activist Mao Hengfeng to a year and a half of labor camp. Mrs. Mao, accused of disturbing social order, was detained in Beijing in late September, said her husband, Wu Xuewei, who indicated she was being put away to silence her before the partycongress.

Even dissidents’ relatives have come under pressure. Beijing activist Hu Jia said that he was warned by police to leave town and that even his parents told him that police had told them to escort him to his hometown.

“My parents said to me, ‘Hu Jia, you don’t know what kind of danger you are in, but we know,’” he recounted in a phone interview from his parents’ home in eastern Anhui province. “They said: ‘Beijing is a cruel battlefield. If you stay here, you will be the first to be sacrificed. Don’t do this.’”