Hong Kong media tycoon and pro-democracy supporter Jimmy Lai has been charged with fraud and detained until a court hearing in April next year.
On Thursday a court denied him bail over a charge relating to the illegal use of his company’s premises.
It comes a day after three prominent pro-democracy activists were jailed.
The arrests have raised fears of a renewed crackdown on the city’s activists and media figures, spurred by a controversial new security law.
China has said the new law will return stability to the territory after a year of unrest, but critics say it has silenced dissent.
Mr Lai, 73, was arrested on Wednesday night along with two other senior executives from media company Next Digital.
Mr Lai is the founder of Next Digital which publishes Apple Daily, a well-read tabloid which is frequently critical of Hong Kong and mainland Chinese leadership.
On Thursday, the three men appeared in court to face charges relating to the alleged illegal usage of their company’s headquarters for purposes not permitted by its lease. No further details were given.
According to an Apple Daily report, the judge presiding over the case had been hand-picked by the city’s leader, Carrie Lam, to handle national security cases.
While the two senior executives were granted bail, Mr Lai was denied because he was deemed an “absconding risk”, according to local reports.
Who is Jimmy Lai?
One of the city’s most prominent supporters of the pro-democracy movement, Mr Lai is estimated to be worth more than $1bn (£766m). Having made his initial fortune in the clothing industry, he later ventured into media and founded Next Digital.
In a local media landscape increasingly fearful of Beijing, Mr Lai is a persistent thorn for China – both through his publications and writing that openly criticises the Chinese leadership.
It has seen him become a hero for many residents in Hong Kong. But on the mainland he is viewed as a “traitor” who threatens Chinese national security.
Earlier this year, he was accused of “colluding with foreign forces” under the new national security law.
He was arrested in August, becoming the most high-profile person in Hong Kong to be detained under the law, and his newspaper offices were raided by hundreds of police officers.
He was later released on bail. However, he told the BBC then the arrest was “just the beginning”.
What’s the situation like in Hong Kong?
On Wednesday, activists Joshua Wong, Ivan Lam and Agnes Chow were jailed for their involvement in mass protests last year.
The young activists – who are among the city’s most prominent – had been convicted of unauthorised assembly.
Rights group Amnesty International condemned the ruling, saying it was a way for authorities to “send a warning to anyone who dares to openly criticise the government that they could be next”.
A former British colony, Hong Kong was handed back to China in 1997 but under the so-called “one country, two systems” principle.
It was supposed to guarantee certain freedoms for the territory – including freedom of assembly and speech, an independent judiciary and some democratic rights – which mainland China does not have.
But the national security law has reduced Hong Kong’s autonomy and made it easier to punish demonstrators.
After the law was introduced, a number of pro-democracy groups disbanded out of fears for their safety.