China jailed democracy activist Zhu Yufu for seven years on Friday for inciting subversion of state power, his wife said, ahead of a high-profile trip to the United States by Vice President Xi Jinping.

Zhu was convicted for collecting donations for relatives of dissidents in jail, publishing a poem online urging people to gather and call for greater freedoms and giving media interviews, rights groups say.

He is the fourth known activist to get an unusually lengthy jail sentence in the space of seven weeks, as China enters a sensitive time ahead of a once-in-a-decade leadership transition due to take place in the autumn.

His sentence also comes ahead of Xi's high-profile visit to the United States, which begins early next week.

"My husband was sentenced for seven years for inciting subversion," Zhu's wife Jiang Hangli told AFP. "I am very surprised about the length of this sentence, it's very unfair."

Jiang said that after the verdict was read out Zhu shouted out that he would appeal the sentence.

Calls to the Hangzhou Intermediate People's Court, where he was sentenced, went unanswered.

The US called for Zhu's release. "We are deeply concerned about these reports that he has been found guilty of inciting subversion of state power and sentenced to seven years in prison for writing a poem," said State Department spokeswoman Victoria Nuland.

Zhu was detained last year as part of a widespread crackdown on dissent that took place in China after anonymous online calls for protests similar to those that swept the Arab world spooked authorities.

He has spent much of the past decade in prison. Between 1999 and 2006, he was jailed for founding a controversial political magazine and served another two years from 2007 after he confronted a policeman who questioned his son.

The poem that got him into trouble this time features the lines, "It's time, Chinese people! The square belongs to everyone. The feet are yours it's time to use your feet and take to the square to make a choice."

Subversion charges are often used to jail government critics. Nobel Peace Prize winner Liu Xiaobo was convicted on the same charge in 2009 and sentenced to 11 years in prison.

Late last year, Chinese courts handed unusually long jail sentences of nine and 10 years to longtime dissidents Chen Wei and Chen Xi, who faced separate subversion charges.

Then in January, Chinese democracy activist Li Tie was sentenced to 10 years in prison, also for subversion.

The Hong Kong-based Information Centre for Human Rights and Democracy condemned the verdict and called on Canadian Prime Minister Stephen Harper, who is currently in China, and Xi's host in the US, Vice President Joe Biden to appeal on Zhu's behalf.

"You must ask directly why Chen Wei, Chen Xi, Li Tie and Zhu Yufu were convicted of 'inciting subversion' for posting a few articles on the Internet," the centre said in a statement.