Hong Kong pro-democracy tycoon Jimmy Lai has been arrested for suspected collusion with foreign forces, his aide has said.
Mark Simon said the businessman was held under the controversial national security law imposed by China in June.
Mr Lai supported pro-democracy protests that erupted in Hong Kong last year.
In February, the businessman was charged with illegal assembly and intimidation. He was later granted police bail.
“Jimmy Lai is being arrested for collusion with foreign powers at this time,” said Mr Simon, an executive at Mr Lai’s media firm Next Digital, which publishes the Apple Daily newspaper.
Hong Kong’s authorities have so far made no public comments on the issue.
The new security law for Hong Kong makes it easier to punish protesters, and reduces the city’s autonomy.
It gives Beijing powers to shape life in Hong Kong, a former British colony, in a way it has never had before.
Critics say it effectively curtails protest and freedom of speech – China has said the new law will return stability to the territory.