A Chinese activist, who was imprisoned after she spoke out about women's rights and Hong Kong's democracy movement, has been released after serving three years in jail, her lawyer said on Thursday.

Su Changlan, a 47-year-old primary school teacher was first detained in southern Guangdong province on October 26, 2014 after making comments on social media in support of democracy protests in the semi-autonomous city of Hong Kong.

“Su Changlan has returned home after her release,” lawyer Liu Xiaoyuan said in a statement on Twitter. Liu has previously claimed that his client was held illegally for years before she was formally convicted and sentenced in March 2017 for “inciting subversion of state power.”

Her case drew international attention at a time when Beijing was reportedly ramping up its crackdown on civil society, targeting everyone from human rights lawyers to celebrity gossip bloggers. More than 200 Chinese lawyers and activists were detained or questioned in a police sweep in 2015 that rights groups called “unprecedented”.

In a statement on Thursday, Amnesty International said that Su's health had deteriorated in “cramped” and “unhygienic” prison conditions, and she now suffers from debilitating heart, liver and gallbladder conditions.

“It's a relief that Su Changlan will not spend another night in jail, but she should never have been denied her freedom in the first place,” said Roseann Rife, Amnesty International's East Asia research director.

“It is imperative that the authorities ensure that Su Changlan can receive the appropriate medical care,” Rife said.

Su could not be reached for comment on Thursday. Lawyer Liu said he didn't have much information about her health problems.

“Her family members informed me and her friends today that Su was released and sent a photo of her. They didn't talk about other things,” Liu told AFP.

Rights groups say a pattern has emerged in recent years where China releases dissidents from prison in poor health, or only weeks before they pass away, with late Nobel laureate Liu Xiaobo being a notable example.

The veteran of the 1989 Tiananmen Square pro-democracy protests died in July, more than a month after he was transferred from prison to a heavily-guarded hospital to be treated for late-stage liver cancer.

Meanwhile, concerns are growing over the whereabouts of book publisher Gui Minhai, who failed to contact his family after Chinese authorities said they had released him from detention on October 17. The Swedish foreign ministry said it had been informed by China of Gui's release and was trying to contact him.

The 53-year-old Swedish citizen and Hong Kong-based publisher, whose company was known for salacious titles about the lives of China's political elite, disappeared in 2015 while on vacation in Thailand.