Hong Kong pro-democracy tycoon Jimmy Lai has been arrested for allegedly collaborating with foreign forces, his aide has said.
Mark Simon said the businessman had been held under the controversial national security law imposed by China in June.
Mr Lai backed the pro-democracy protests that erupted in Hong Kong last year.
In February, the 71-year-old mogul was charged with illegal assembly and intimidation. He was later released on bail by police.
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“Jimmy Lai is being arrested for collaborating with foreign powers at this time,” said Mr Simon, an executive at Mr Lai’s media firm, Next Digital.
Hong Kong authorities have so far made no public comment on the matter.
Who is Jimmy Lai?
Mr Lai is estimated to be worth more than $ 1bn (766m).
The newspaper he founded, Apple Daily, is often critical of Hong Kong and the Chinese leadership.
“The establishment hates my hatreds,” Mr. Lai said earlier in an interview with the New York Times. “They think I’m a problem.”
And on June 30, when the security law was passed, the businessman told the BBC that it “predicts the knee of death for Hong Kong”.
He warned that Hong Kong would become as corrupt as mainland China because “without the rule of law, people doing business here would have no protection.”
In an exclusive interview with the AFP news agency, Mr Lai said: “I am prepared for prison. If he comes, I will have the opportunity to read books I have not read. The only thing I can do is be positive. “
What is the new security law?
The law makes it easier to punish protesters and reduces Hong Kong autonomy.
It also empowers Beijing to shape life in the former British colony in a way never before.
Critics say it effectively restricts protest and freedom of speech – China has said the new law will restore stability to the territory.
Key provisions of the law include that crimes of secession, destruction, terrorism, and cooperation with foreign forces are punishable by a maximum life sentence in prison.