SHANGHAI: A prominent newspaper columnist who challenged government censors by writing about corruption and political reform was dismissed on Thursday by the Southern Daily Group, publisher of some of the country's best-known newspapers.

The columnist, Chang Ping, said he was forced out because his bosses were ''under pressure'' from government propaganda authorities.

The executive editor, Zhuang Shenzhi, said that the publisher had decided not to extend Chang's contract. ''The paper thought some of his work was inappropriate,'' Zhuang said.

Chang's departure has raised concerns that authorities, who already censor publications and broadcasts heavily and commonly dismiss reporters and editors who defy censors, are clamping down harder on China's increasingly independent-minded press.

Chang, 42, has a reputation for writing about politically sensitive topics, including democracy, media censorship, the failures of government policy and Tibet. His commentaries appeared in Southern Weekend and Southern Metropolis Daily, both published by the Southern Daily Group.

''Now I have 'been resigned'. It is not just because of one particular article, it is because I have always written critical articles,'' Chang said. ''Many times I have been told not to write and that if I agreed I would be able to get more benefits than now, but I refused. The reason the paper is giving is that 'pressure from above is too great'.''

A 2008 commentary by Chang that carried the headline Tibet: Nationalist Sentiment and the Truth enraged nationalists who supported a crackdown on what the government called separatist activities in Tibet. Chang also wrote and lectured about media censorship and civil society. In a recent lecture at Fudan University in Shanghai he said, ''We should transform into a civil society rather than wait for a virtuous leader.''

He also said: ''Society is diverse and should have a platform for giving opinions. We don't necessarily need everyone to support freedom and democracy. What is key is whether these opinions are people's own voices.''

Chang was removed in late 2008 from his position as deputy chief editor of Southern Metropolis Daily and was also dismissed as a commentator. But he retained a research position at the Southern Daily Group and continued to write for other publications.

He said he believed he was dismissed because ''the media censorship has tightened since the Nobel Peace Prize'', referring to the government's anger over the decision to award the prize this year to an imprisoned dissident, Liu Xiaobo.

''I will keep writing,'' he said. ''I won't stop.''