The Hong Kong-based publisher disappeared in 2015 while on holiday in Thailand. He was held at an undisclosed location in China until he was formally released in October last year. However, his daughter Angela Gui said at the time his freedom of movement remained restricted and he was being kept in China.
The New York Times reported on Monday that Gui, 53, had been on board a train to Beijing to undergo a medical examination at the Swedish Embassy after showing symptoms of ALS, a disease which attacks the brain and spinal cord, when ten men stormed the train at a station and took him with them.
This is said to have happened in front of two Swedish diplomats from Sweden's Shanghai consulate.
“I just know that things have taken a very drastic turn for the worse,” Angela Gui told The New York Times.
“This group of about 10 men in plain clothes just came in and grabbed him from the train and took him away,” she told the newspaper. “I presume it must have been quite a scene.”
The New York Times labelled the men police officers, but Angela Gui said she did not know which branch of the Chinese police or security forces was responsible for her father's most recent abduction.
She also said she did not know whether or not the diplomats attempted to resist the arrest. The Swedish Foreign Ministry confirmed that there had been an incident on Saturday, but offered no details and declined to say when approached by Swedish media if Chinese authorities had informed them.
“The Swedish government is fully aware of what happened to Swedish citizen Gui Minhai on Saturday,” spokesperson Katarina Byrenius Roslund told The New York Times.
“These events have subsequently been handled with the utmost seriousness, and robust measures have been taken at senior political level.”
Foreign Minister Margot Wallström told Swedish news agency TT that she had summoned China's ambassador to demand more information, but declined to comment further at this stage “out of consideration for” Gui.
The Chinese Foreign Ministry said it had “no understanding of the situation you referred to” when approached by The New York Times.
Gui, who went to study in Sweden in 1988 and became a citizen in 1992, was one of five Hong Kong booksellers known for publishing gossipy titles about Chinese political leaders to go missing in 2015.
In 2016, he resurfaced on Chinese television saying he had returned to take responsibility for his involvement in a fatal car accident years before in Zheijiang province, a confession dismissed by human rights campaigners. The other four people have been released.