BEIJING — Perched unsteadily on a stack of plastic stools in an isolated room, Xie Yang, a Chinese lawyer, was encircled day and night by interrogators who blew smoke in his face, punched and kicked him, and threatened to turn him into an “invalid” unless he confessed to political crimes, he has said.

Eventually, according to transcripts of meetings with Mr. Xie issued by his attorneys, the isolation, sleepless days and nights of abuse and threats to his family from the police investigators proved too harrowing. Mr. Xie said he had scribbled down whatever they told him to say about trying to subvert the Chinese Communist Party by representing disgruntled citizens and discussing rights cases.

“I wanted to end their interrogation of me as quickly as I could, even if it meant death,” Mr. Xie, anguished and often sobbing, told his attorneys, Chen Jiangang and Liu Zhengqing, according to the transcripts of the meetings this month that Mr. Chen released on Thursday. “Later, I wrote down whatever they wanted.”

The records lay out the most detailed firsthand allegations thus far that torture has stained a crackdown on Chinese rights lawyers and advocates that began in July 2015. The government detained almost 250 people in that operation, according to Amnesty International. Most were released, but four were tried and convicted last year on charges that they tried to subvert the one-party state, and about 13 are in detention and likely to face trial.

Mr. Xie, 44, a lawyer from the southern Chinese province of Hunan, is also likely to face trial in the coming weeks on subversion charges, according to his lawyers.

“These transcripts are totally authentic,” Mr. Chen said in a telephone interview on Friday, referring to two detailed records of pretrial meetings with Mr. Xie that were released on overseas websites focused on human rights in China. “He’s suffered torment and abuse, and this was a call for help, because the internal mechanisms for preventing torture haven’t worked.”

Other defendants and suspects in the clampdown on rights lawyers have abjectly declared their guilt, either in court or in televised confessions. Mr. Chen said that Mr. Xie wanted to release his account of his secretive detention to prove beforehand that he was innocent and that any admissions had been made under coercion.

“He was unbending. He refused all government lawyers. In the end, they had to let us see him,” Mr. Chen said, since he and Mr. Liu had been chosen by Mr. Xie. “We all know this kind of case is about political persecution.”

Mr. Xie’s wife, Chen Guiqiu, had also approved releasing the transcripts, Mr. Chen said. But Ms. Chen, an academic, did not answer repeated calls to her phone on Friday. Mr. Chen, the lawyer, said she had been led away that morning by security guards at the university in Changsha, the capital of Hunan, where she works.

“Let the world know what forced confession through torture is, what shamelessness without limit is,” Ms. Chen said in a statement issued on Thursday.

Mr. Xie’s account of being locked away appeared after China’s president, Xi Jinping, sought this week to promote his government as open and mature. On Tuesday, Mr. Xi told the World Economic Forum in Davos, Switzerland, that economic protectionism was like a country locking itself in a dark room.

Li Chunfu, a Beijing lawyer detained in the crackdown, was released early this month, emaciated and mentally shattered after nearly one and a half years in detention, according to his family and supporters.

“It’s ironic that the Chinese government is calling for openness in Davos when the Chinese government is doing the opposite domestically,” Maya Wang, a researcher on China for Human Rights Watch, said by telephone from Hong Kong. “They say one thing in terms of rhetoric, to appeal and charm globally, but what they do is quite another thing. What they do is exactly the opposite.”

Human rights organizations and defense lawyers have said that other suspects caught in the crackdown have also been at risk of torture while in secretive detention. The Chinese government has repeatedly denied such accusations. The police in Changsha did not respond to multiple phone calls to find out whether they knew of Mr. Xie’s allegations of torture and were doing anything about them.

But Mr. Xie has gone to extraordinary lengths to back his claims: He named many of the officers he says perpetrated abuses. “If I stand trial, I’ll recount to the court just what happened in this case — that the records were the product of torture,” he told his lawyers.

Mr. Xie was taken away by the police in Hunan on July 11, 2015, and spent half a year in secretive detention in a retired military cadres’ hostel, kept from contact with the outside world. In the first week, Mr. Xie said, he was questioned by rotating teams of officers who gave him no more than three hours of sleep between grueling rounds of questioning.

Often they made Mr. Xie sit on top of the “dangling chair”: several plastic stools without backrests that were stacked on top of each other.

“I sat on top so that my feet didn’t touch the ground and my legs were dangling there. They ordered me to sit there with my back straight,” he said. He said that an officer warned him: “If you move, we can consider that you attacked a police officer, and we can take whatever steps to deal with you.”

In addition, the interrogators would not let him drink water, lit fistfuls of cigarettes and blew nauseating clouds of smoke in his face, and beat, kicked and head-butted him, he said. They also indirectly threatened his wife, warning that she should be careful when driving, he said.

“We represent the party center in handling your case,” one police officer said, referring to China’s central leadership, according to Mr. Xie’s account. “Even if we leave you dead, you won’t find any evidence to prove it.”

By mid-August 2015, Mr. Xie said, he was broken, and he signed documents put before him, but still he resisted the interrogators’ demands that he name and implicate other people. A year ago, he was formally arrested on a charge of inciting subversion of state power and was moved to a detention center. But there, the abuses continued, and other detainees were used to bully him, Mr. Xie said.

Despite pressure from the police and prosecutors, Mr. Xie insisted on seeing his own lawyers. On Friday, they asked prosecutors to examine his claims of torture, listing the names of 10 police officers they say should answer the accusations.

“I tell you now that my spirit is free,” Mr. Xie told his lawyers. “I declare that I, Xie Yang, am innocent.”