Two prominent Chinese political activists went on trial Friday for helping to organise small-scale protests against censorship, their lawyer said, the latest prosecution in a deepening government crackdown on dissent.

Guo Feixiong and Sun Desheng both face possible five-year prison sentences for their attempts to raise awareness of press freedom and human rights, their lawyer Li Jinxing told AFP.

The pair are the latest in a wave of human rights activists, lawyers, academics and journalists to be jailed or detained in what has been seen as China's biggest campaign against government critics in years.

Both are writers best known by their pen-names and at a court in the southern city of Guangzhou, Guo, whose real name is Yang Maodong, and Sun, whose real name is Sun Sihuo denied "gathering a crowd to disturb public order", a charge often used to jail protesters.

A verdict will be announced at a later date, Li added. China's courts, controlled by the ruling Communist Party, have a near-100 percent conviction rate in criminal cases and the pair are almost certain to be found guilty.

The trial was still ongoing Friday night, Li told AFP during a break in proceedings.

He said the lawyers and defendants had complained to the court about what he called the "inhuman" nature of the long session that started at 9.00 am (0100 GMT).

Li said that though a 30-minute meal break had been allowed during the day, the court wanted to continue without one in the evening but relented after the defence demanded one.

It was unclear how late the session would continue, he added.

- Silence human rights advocates -

Prosecutors at the hearing said the activists' support for protests against censorship at a liberal southern Chinese newspaper last year make them eligible for the maximum sentence, Li said.

"Guo wanted to push forward the progress of society peacefully and rationally, but despite that, the authorities could not accept this," Li said. "This is a problem for all Chinese people."

Prosecution documents also mentioned an "advocacy tour" last year which saw activists travelling across China to promote awareness of human rights, the US-based Chinese Human Rights Defenders (CHRD) said.

Four other activists involved in the tour have also been detained, the CHRD said, in what it called a "major crackdown" under President Xi Jinping.

The trial shows that "the government under Xi's leadership has no intention to loosen its control on the legal system as its weapon to silence and punish human rights and democracy advocates", CHRD researcher Renee Xia said in a statement.

Human Rights watch researcher Sophie Richardson said in a statement that "Beijing's assault on civil society seems to know no bounds as peaceful activists are increasingly subject to criminal prosecutions."

Guo, a legal consultant based in Guangzhou, is well-known after helping residents of a southern Chinese village organise in 2006 against a local Communist Party boss who they accused of illegally selling their land to enrich himself.

Guo has been kept under detention for 15 months following his involvement in rare protests which saw around 100 people gather outside the offices of the Southern Weekly newspaper in January last year after one of its editorials was heavily censored.

China has this year used the same charge faced by Guo and Sun to jail around a dozen activists who held small-scale protests calling for officials to disclose their financial assets as a measure against corruption.