Gui, one of five Hong Kong-based booksellers known for publishing salacious titles about China's political leaders, has been at the centre of diplomatic tensions between Stockholm and Beijing for a decade.

China accuses Gui of illegally providing intelligence abroad.

"I have been very clear about the fact that the Swedish government demands the release of Gui Minhai and that he should be reunited with his daughter and the rest of his family," Foreign Minister Maria Malmer Stenergard told Swedish public broadcaster Sveriges Radio while in Beijing, where she met with her Chinese counterpart, Wang Yi.

She said neither she nor Swedish embassy officials had been allowed contact with Gui.

"I have no detailed information (on how he is doing), but I can't go into any details out of consideration for Gui Minhai," she said.

Gui disappeared while on holiday in Thailand on October 17, 2015 -- exactly 10 years ago -- and resurfaced in China, where he served two years in prison.

A few months after his October 2017 release, he was again arrested, this time while on a train to Beijing with Swedish diplomats.

He was then hit with the 10-year jail term in 2020.

Gui Minhai was born in China but moved to Scandinavia following the Tiananmen crackdown in 1989, and later became a Swedish citizen.

Sweden has repeatedly called for his release.

Beijing insists the matter is an internal affair and has rejected Sweden's criticism.

China does not recognise dual citizenship, and Chinese officials claimed he voluntarily reinstated his Chinese citizenship in 2018.

Sweden insists he remains a citizen.

Malmer Stenergard's visit to China was the first by a Swedish foreign minister in 11 years, she said.