An activist accused of subversion, damaging national security and harming social stability pleaded guilty as a high-profile trial got under way at Tianjin No 2 Intermediate People's Court on Tuesday.

Zhai Yanmin is accused of posting statements and comments online since 2012 in a bid to subvert State power.

He allegedly joined an "underground organization", led by another man named Hu Shigen, which guided residents to instigate others and disturb public order, according to prosecutors from Tianjin's No 2 People's Procuratorate.

During the trial, Zhai admitted that he and lawyer Zhou Shifeng hired people who posed as protesters to shout slogans and hold signs in support of the latter while he was in court.

"The organization was not registered. During our discussions, it was Hu who usually came up with the ideas, and such ideas were usually harmful to the country," Zhai said in court. "At that time, I agreed with Hu."

"Zhou and I had followed hot topics online closely, aiming to take advantage of them to manipulate public opinion," he added.

Hu and Zhou are being prosecuted in separate cases.

Zhai's case is still being heard and no verdict has yet been given.