The trial of a prominent Chinese human rights lawyer has begun without prior public notice.

Monday's development follows delayed proceedings in the case, which has prompted international concern after allegations that he had been tortured.

Xie Yang, who had worked on numerous cases considered politically sensitive by China's ruling Communist Party, was among hundreds of legal staff and activists detained in a crackdown in the summer of 2015.

"On May 8 at 9:30am, the trial of defendant Xie Yang opened. [He] is charged with inciting subversion of state power and disrupting court order," the Changsha Intermediate People's Court said in an online statement.

The court also posted what appeared to be a transcript of opening proceedings.

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Last-minute delays or sudden announcements of sensitive trials are not uncommon, even though Chinese law requires courts to give a defendant's family and lawyers three days notice of any changes.

On April 25, dozens of supporters and at least seven diplomats had gathered at the Changsha court in central Hunan province - a long way from Beijing and Shanghai - only to be told the trial was indefinitely postponed.

Since they received no confirmation of the new trial date, diplomatic sources told AFP news agency they were not prepared to head to remote Changsha again to observe the trial.

Local activists said in social media posts that they were "warned" on Sunday not to go to Changsha, without providing details about the warnings.

A 'pattern of harassment'

Xie says police have used "sleep deprivation, long interrogations, beatings, death threats, humiliations" on him, and the European Union has voiced concern over his case.

Eleven countries, including Canada, Australia and Switzerland, have cited Xie's case in a letter to Beijing criticising China's detention practices.

Xie's former lawyer, Chen Jiangang, was detained by authorities last week while he was vacationing with his family, prompting condemnation from the UN's human rights office.

A UN statement on Friday said the move was part of a "continuing pattern of harassment of lawyers, through continued detention, without full due process".

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The vast majority of detained lawyers were defending citizens' basic economic, social and cultural rights, the UN said.

Chen had remained vocal on Xie's case, drawing attention to his former client's allegations of torture, even after the Changsha court denied Xie his pick of defence and provided a court-appointed lawyer instead.

In March, state media accused Chen along with another prominent rights lawyer, Jiang Tianyong, of fabricating detailed accounts of torture suffered by Xie Yang, saying they had made up "fake news" to grab international headlines.

Chen at the time told Reuters that the accounts were genuine, saying he had interviewed Xie in rooms filled with cameras.

Xie's new defence lawyers have not answered calls from AFP.

Source: News agencies