The wife and son of outspoken former Chinese professor Guo Quan, who is serving a 10-year sentence for "subversion", have left China for a new life in the United States, a rights group said Tuesday.

The news comes days after Yu Jie, a famous writer who defiantly published a critical biography of Premier Wen Jiabao in 2010 in Hong Kong, also fled into exile in the United States after he was physically abused by authorities.

Li Jing and the 12-year-old Guo Yi arrived in Los Angeles on Monday by plane to start a new life in the United States, the US-based ChinaAid group said in a statement emailed to AFP.

"They will be appealing to the US government and international groups to pay close attention to Guos case and for help in winning his release," the group said, without providing further details.

Guo -- a former university professor in eastern China -- was jailed in October 2009 for "subversion of state power."

He was an outspoken critic of the Chinese government and also advocated a "multi-party, competitively elected democratic system", according to the US-based Human Rights in China.

He was stripped of his position by Nanjing Normal University in late 2007, and was arrested the following year after publishing articles and letters online addressed to President Hu Jintao and other leaders.

"Subversion of state power" is a charge that critics of China's ruling Communist Party -- which maintains a firm grip on all political activity in the country -- say is often used to silence dissenters.

Li and Guo's exile comes at a sensitive time in China, which is preparing for a major leadership transition in the autumn that has triggered official concern about anything that could provoke unrest in the country.

Three activists were recently jailed in the space of just one month for nine to 10 years -- all for subversion.

Rights groups and Western government have also voiced concern about other dissidents in China including Chen Guangcheng, a blind self-taught lawyer who uncovered alleged forced abortions under the country's one-child policy.