A human rights lawyer who represented Ai Weiwei against the Chinese government has "disappeared" after trying to board a train to the southern province of Guangdong, according to rights activists.

Liu Xiaoyuan was stopped by police on March 1 as he tried to travel to Zhuhai city from Ganzhou in the eastern province of Jiangxi, the Weiquanwang rights website reported.

"I was stopped by police from the Ganzhou West Railway Station public security station in Jiangxi province, en route to Zhuhai," Liu wrote in a WeChat post before going incommunicado.

"I asked for a written record [of this interaction], but they refused."

The incident comes as China has stepped up detentions of dissidents and religious figures ahead of the annual session of its rubber-stamp parliament, the National People's Congress.

Liu, a former member of the now-shuttered public interest law firm Beijing Fengrui, went incommunicado on the eve of the annual session in Beijing, a time when the authorities typically target critics of the ruling Chinese Communist Party.

The lawyer previously represented Ai Weiwei when the globally renowned artist was detained in 2011. Ai once called him “the best lawyer in China”.

Other clients have included journalists and activists accused of subverting the Chinese Communist Party.

Stopped by rail police

Before going missing, Liu wrote that he had been stopped by rail police while attempting to travel.

The Civil Rights and Livelihood Watch website also reported concerns about Liu's whereabouts, tweeting a message from the lawyer on the day of his "disappearance."

"My ID card showed up as invalid when I went through the [automatic security] gates, and it wouldn't let me through with just a train ticket," Liu said in comments posted by the group to Twitter.

"Then four railway policemen surrounded me and wouldn't let me go, and the duty supervisor even wanted to confiscate my ID card," he wrote.

"[They said] they were assisting the state security police in my hometown of Suichuan county with their investigation," Liu said.

A fellow rights lawyer who asked to remain anonymous confirmed the rights groups' accounts.

"Liu [told me] last night that he didn't eat, because he was waiting for them to give him an explanation," the lawyer said. "I haven't been able to contact him since [Wednesday] afternoon."

"His mobile phone is switched on, but nobody is picking up," he said.

He said Liu has been repeatedly harassed and persecuted by the government since he was targeted in a 2015 nationwide police operation that saw hundreds of lawyers, law firm staff and rights activists detained, hauled in for questioning and even jailed for subversion.

Stripped of license

Authorities in Beijing stripped Liu of his license to practice as a lawyer in October 2019 after he published a photo of himself selling insecticide as a street vendor - an image that could be considered “a kind of art…[and] a complaint against the abuse of power” by authorities who had forced the shutdown of his law firm he told RFA at the time.

An employee who answered the phone at the Ganzhou municipal railway police department declined to comment when contacted by Radio Free Asia on Thursday about Liu’s disappearance.

Meanwhile, veteran journalist Gao Yu has been taken to the eastern province of Shandong under police escort, while police in the southwestern province of Guizhou have placed more than a dozen members of the banned Guizhou Human Rights Forum under detention or house arrest, activists told Radio Free Asia.

Prominent dissidents Zha Jianguo and Ji Feng are both under house arrest or close surveillance, as is rights activist Li Wei, who posted that he was "going out to walk around and shop, with personal carers alongside," in an apparent reference to state security police minders.

Guizhou rights activists Chen Xi, Li Renke, Liao Shuangyuan, and Shen Youlian have all been placed under close surveillance, while a local Protestant church member said Guizhou pastor Yang Hua is currently under travel restrictions that will likely end in mid-March, after the National People's Congress closes.