Gui, who has Swedish citizenship, was taken away on Saturday by plainclothes police officers as he travelled by train to Beijing, in the company of two Swedish diplomats, The New York Times said.
Gui was first abducted on holiday in Thailand in 2015, one of five Hong Kong booksellers who went missing that year and later appeared in mainland Chinese custody.
He was held for publishing books on the personal lives of Communist Party leaders. Chinese authorities said he was released in October last year, although his whereabouts remained unclear.
A Swedish Foreign Ministry official would not comment on what had happened but said Sweden was aware and would be able to provide more information, probably later on Monday.
“The Swedish Government is fully aware of what happened on January 20. Firm actions have been taken at a high political level and we have been in contact with Chinese officials who have promised us immediate information about his condition,” Patric Nilsson said.
Gui Minhai had been kept in China and forced to report regularly to the police, his daughter, Angela Gui, told the New York Times by phone from the United Kingdom, where she is a graduate student.
Chinese authorities have said Gui was involved in a traffic accident in 2003, although that has been questioned by his family.
China’s foreign ministry did not immediately respond to a request for comment.