A court in Tianjin sentenced activist Zhai Yanmin to three years in prison with a four-year reprieve on Tuesday for subverting state power.

Zhai, an unemployed resident of Beijing, used the internet to post statements and comments that harmed national security and social stability, according to the verdict handed down by Tianjin No 2 Intermediate People's Court.

Zhai, 55, pleaded guilty during the open trial. "I accept the verdict and will not appeal," he said.

The verdict stated that Zhai began using online posts in 2012, manipulated public opinion and organized protests after he joined an unregistered "underground organization" led by another man, Hu Shigen.

Zhai also colluded with lawyers, including Zhou Shifeng, and hired people to play up hot online issues or cases to disturb public order by shouting slogans and displaying signs, the verdict stated.

For example, a man was shot dead after attacking a police officer at a railway station in Qing'an county, Heilongjiang province, on May 2 last year, triggering public attention.

Zhai, incited by Hu, published online statements to confuse the issue. He also arranged for several people to go to the railway station to display banners with anti-government slogans and to distribute leaflets outside the county government headquarters, according to the verdict.

Prosecutors said that Zhai, together with Hu, Zhou and Li Heping, conspired and plotted to subvert state power, and had "established a systematic ideology, method and steps to achieve it".

Hu, Zhou and Li are being prosecuted in separate cases.

"All Zhai's behavior constituted the crime of subversion," Cai Shuying, the trial judge, said.

But the court had given Zhai a lenient punishment as he had pleaded guilty and had cooperated after his arrest, the judge said.

A three-year sentence with a four-year reprieve means he will not be imprisoned if he behaves well and commits no other offenses during the reprieve period.

About 50 people, including law professors, attorneys and journalists, attended Tuesday's trial.

Ruan Chuansheng, a criminal lawyer from Shanghai who has kept a close watch on the case, said punishing those who use the internet to commit crimes is "a must" for a country ruled by law.

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