Police and men in plainclothes scuffled with supporters of one of China's most celebrated human rights lawyers Monday as he was tried over online comments critical of the ruling Communist Party.

Dozens of Pu Zhiqiang's supporters travelled from across the country, some for thousands of kilometres, to protest outside the courtroom in Beijing.

The crowd was shoved hundreds of metres away. "Pu Zhiqiang! Innocent!" protesters shouted 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, and shoved at least two to the ground.

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

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 little more than three hours, he said Beijing's Number Two Intermediate People's Court considered the evidence -- seven posts Pu made on a microblog between 2011 and 2014.

According to Mo, his client told the court he was willing to apologise to anyone who had been harmed by his comments.

"I am a man of the law," the lawyer quoted Pu as saying. "I have faith in the law, so I believe and hope that the court can give me a verdict that can stand the test of history."

No ruling was issued Monday but Mo said he expected it "quite quickly".

Supporter Bao Renpu condemned the strong-arm tactics against the crowd.

"On the outside, the government talks about human rights and democracy, but on the inside, it simply doesn't exist," she said.

Security personnel -- those in civilian dress identifiable by "smiley face" stickers on their clothing -- also pushed and shouted at senior US diplomat Dan Biers and journalists.

"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.

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

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

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

- 'A good man' -

In the comments for which he was tried, Pu said 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."

The 50-year-old 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.

He is virtually certain to be convicted in the Communist-controlled court.

A former client of his, Xie Sunming, told AFP: "Sure, they won't let us into the courtroom, but that's not what's important. I'm here to support Pu Zhiqiang, a good man who helped me immensely."

Xie was sentenced to a year in a labour camp in 2009 for posting a single sentence on an online forum accusing a local government official of corrupt business ties.

He drove 20 hours from Chongqing in southwestern China to stand outside the Beijing courthouse, saying he and a friend "had to sneak out and drive all night", unable to travel by air or train for fear of being detained.

The US embassy said in a statement it viewed "with great concern" incidents in which diplomats were not given appropriate protection and respect.

China's foreign ministry said authorities functioned "in accordance with the law" and "people should cooperate with them".

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