Close friends Gao Yu, a veteran journalist in Beijing, and Wu Yangwei, better known by his penname Ye Du, said Liu Xia was on a Finnair flight to Berlin that left Tuesday morning.
A friend of Liu Xia told Reuters in May that she was losing hope of leaving the country.
It's been nearly a year since Nobel peace prize victor, writer, and human rights activist Liu Xiaobo passed away of liver cancer in custody in China, with Beijing rejecting pleas for the dissident to be allowed to travel overseas for treatment.
Liu's release comes as Chinese Premier Li Keqiang is visiting Germany, a country that in May said it would welcome the widow after a recording was released of her crying in desperation and indicating she has given up hope of being able to leave China. He thanked everyone who had cared for and helped her over the years.
Liu Xia had left to "start her new life" in Europe, her younger brother, Liu Hui, said on his WeChat account, according to a screenshot of the message shown to Reuters by a friend who declined to be identified. Hong Kong-based South China Morning Post later said it had also independently confirmed her departure.
In a July 2017 photo released by the Shenyang Municipal Information Office, Liu Xia, wife of jailed Nobel Peace Prize victor and Chinese dissident Liu Xiaobo, holds a portrait of him during his funeral at a funeral parlor in Shenyang in northeastern China's Liaoning Province.
The reports of Liu Xia's departure come as Li wraps up a two-day visit to Germany.
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On Chinese social media, some are expressing their happiness for her-obliquely, of course, so as to avoid censorship. He had been sentenced to 11 years in 2009 on subversion charges.
In an emotional phone call with her friend Liao recently, Liu said, "they should add a line to the constitution: "Loving Liu Xiaobo is a serious crime - it's a life sentence".
"It is wonderful news that Liu Xia is finally free and that her persecution and illegal detention at the hands of the Chinese authorities has come to an end, almost one year since Liu Xiaobo's untimely and undignified death", Patrick Poon, China Researcher at Amnesty said in a statement he sent to Al Jazeera. "China hopes to team up with Germany", he said.
It's also a big win for Germany, one of the few countries allowed to send a doctor to China a year ago to examine Liu Xiaobo.
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.
In May, several foreign diplomats who tried to visit her at her apartment amid concerns over her health were denied access.
An accomplished artist and poet, Liu told Associated Press reporters during an unexpected visit to her home in 2012 that she had anticipated China would punish her for her husband's Nobel award but she had not expected to be kept under "Kafkaesque" house arrest.