Ms Liu's departure was "wonderful news" but harassment of her family remained a risk to her freedom to criticise China, Amnesty International's China researcher Patrick Poon said.
A poet, a painter, and a photographer herself, Liu Xia's writings are inward-looking, wrote Ian Johnson, noting that her poems are laden with symbols associated with the struggles of dissidents in China, such as birds and the empty chair that has come to to represent Liu Xiaobo.
Hua Chunying, a Chinese foreign ministry spokeswoman, said that Liu's travel to Germany for medical treatment was "of her own free will".
While precise details of Liu's flight out of China are unknown, the only Finnair flight that left Beijing Capital International Airport bound for Berlin on Tuesday morning was Flight AY86, which took off at 10.55am, according to the airport's website.
China sentenced Liu Xiaobo in December 2009 to 11 years imprisonment on charges of inciting subversion of state power after he helped write a manifesto calling for political and economic liberalization.
Friends of Liu Xia had expressed concern for her mental health ahead of the first anniversary of her husband's death on Friday. Apart from Liu Xia, everyone is also very anxious about [detained human rights lawyer] Wang Quanzhang. German Chancellor Angela Merkel meets regularly with dissidents during visits to China and has raised Liu Xia's case with Chinese officials, including during a visit in May, people familiar with the matter said.
In May, dozens of the world's leading writers and artists, from Michael Chabon to Paul Auster and Khaled Hosseini, called on China to release her to seek medical treatment overseas.
George Clooney reportedly hurt in motorcycle crash in Italy George Clooney has been injured after a motorcyle he was riding collided with a pickup truck in Sardinia, Italian media reports. Clooney was travelling towards the set in Costa Corallina when a vehicle suddenly turned and struck him, according to La Nuova.
The post was verified by two of Liu Xia's close friends.
"I don't see any association or link between this incident and the visit paid by Premier Li", said Hua.
Germany and the United States both sent doctors to visit Liu Xiaobo during his last days.
He said her health and mental state were "not ideal" as she was heavily affected by the death of their parents and her husband: "I hope after she gets out, she can look after her health and her emotional state, and then slowly begin her new life".
Her younger brother, Liu Hui, is in China.
Chinese authorities had consistently maintained Liu was free but imposed severe restrictions on her movement and she was under constant surveillance.
After years of living under house arrest Liu Xia suffers from clinical depression and her friends said last year that she required medication just to be able to sleep at night.
Another friend, Ye Du, told the Post that Liu Xia's elder brother, Liu Tong, told him over the telephone that he was very happy that his sister had left China. "It would be most callous of the Chinese authorities to use Liu Xia's relatives to put pressure on Liu Xia to prevent her speaking out in the future".