Rare video footage of Liu Xia, the wife of imprisoned Chinese Nobel laureate Liu Xiaobo, reading two self-written poems under house arrest was posted online Wednesday.

Chinese authorities have not charged Liu Xia with any crime but have restricted her to her home in Beijing since 2010 when her husband -- an outspoken advocate of democratic reform -- was awarded the Nobel peace prize, following his jailing.

He was sentenced to 11 years in prison in 2009 on subversion charges after co-authoring Charter 08, a bold petition calling for political reform in his Communist-ruled homeland.

A video of Liu filmed at home reading two poems was posted to the video-sharing site Youtube by China's Independent PEN Centre, a group of writers advocating freedom of expression in the Communist-ruled country.

She appeared thin and smoked a cigarette as she read the two pieces, one appearing to reference her house arrest, which has seen her leave home just a handful of times in recent years under police escort and raised concerns about her mental condition.

"Is it a tree? It's me, alone," she read in a quiet but determined voice. "Even when exhausted, I want to stand/Is there anyone with you?"

She followed the poem with a brief thumbs-up to an anonymous camera operator.

Liu Xia has suffered increasing depression since 2009 and her mental state is "very bad", the political activist Hu Jia, who is a friend of hers, told AFP last month.

Liu was allowed to leave her house for brief periods last year to attend the trial on fraud charges of her brother Liu Hui, who was sentenced to 11 years' jail in a case that relatives and lawyers said was politically-motivated retaliation against the family.

"I have lost all of my personal freedom," she wrote in a letter posted online by her lawyer last year, adding: "Perhaps in this country being the wife of Liu Xiaobo is a kind of crime."