BEIJING (AFP, Reuters) - One of China's most celebrated human rights lawyers went on trial on Monday (Dec 14) over online comments critical of the ruling Communist Party, as the police scuffled with supporters and journalists gathered outside the courthouse.

Pu Zhiqiang, who has represented labour camp victims and dissident artist Ai Weiwei, was detained a year and a half ago in a nationwide crackdown on dissent.

He faces a maximum of eight years in jail on charges of "inciting ethnic hatred" and "picking quarrels and provoking trouble", according to his lawyer Mo Shaoping.

In a trial that lasted less than four hours, another defence lawyer Si Weijiang said Beijing's Number Two Intermediate People's Court considered the evidence - seven posts Pu made on a microblog between 2011 and 2014. No verdict was immediately issued.

In the comments, Pu said that China did not need Communist rule, writing: "Other than secrecy, cheating, passing the buck, delay, the hammer and sickle, what kinds of secrets of governance does this party have?"

He also condemned government policy in the mainly Muslim far western region of Xinjiang as "absurd" in the wake of a bloody knife attack blamed on separatists that killed 31 people at a train station in Kunming.

"Don't be a conqueror or a plunderer," he wrote. "No matter whether your aggression is a preemptive measure or a responsive measure, it's all aggression. It's all about making the other side your enemy."

Dozens of supporters travelled from across the country, some for thousands of kilometres, to protest outside the courtroom. Police repeatedly clashed with them, with officers and men in civilian dress - identified by "smiley face" stickers on their clothing - pushing them hundreds of metres away.

The crowd shouted " Pu Zhiqiang! Innocent!" before being broken up by police who said they had obstructed the pavement. Authorities dragged at least three people away, an AFP reporter at the scene saw.

They pushed and shouted at senior US diplomat Dan Biers so forcefully as he tried to read a statement condemning the trial that the scrum around him had relocate multiple times.

"Lawyers and civil society leaders such as Mr Pu should not be subject to continuing repression but should be allowed to contribute to the building of a prosperous and stable China," Biers said. "We urge Chinese authorities to release Mr Pu and call upon China to uphold fundamental civil rights."

A diplomat from the European Union mission was also pushed and shouted down as he delivered a statement criticising the process.

"When you come to China, you need to respect China's laws," one officer told foreign journalists as he punched his way forward.

Police stationed outside the courthouse clashed with Pu's supporters and authorities dragged at least three people away, an AFP reporter at the scene saw.

"China has too few good lawyers - he was one of the few," Mr Yao Lianshe, a citizen who goes to as many trials as he can despite frequent police harassment, told AFP.

"Nothing in China will ever change for the better unless the people are unafraid to stand up to authority and bear witness."

Pu, 50, is the latest person to be tried in a crackdown on critics of the Communist Party overseen by President Xi Jinping, which has seen hundreds detained and dozens sent to prison.

His case will be seen by rights groups and the West as a measure of what they say is the most severe clampdown on human rights in two decades in China.

" Pu's trial is extremely important - he's the ultimate canary in the coalmine," said Maya Wang, a China researcher for Human Rights Watch. "If they decide to be harsh against him, I'd say it'll signify a further escalation of hostility towards human rights activism."

Pu has represented many well-known dissidents, including artist Ai Weiwei and activists of the "New Citizens' Movement", a group that has called on Chinese leaders to make their wealth public.