Hong Kong media tycoon and Beijing critic Jimmy Lai was charged under a new national security law Friday, accused of colluding with foreign forces, the latest pro-democracy figure targeted under the legislation.

Lai, 73, is the most high-profile figure charged under the sweeping law, which has targeted the city's pro-democracy movement but brought a semblance of calm to the finance hub after months of often-violent protests.

The city's new national security unit charged him "with one count of 'collusion with a foreign country or with external elements to endanger national security'", police said in a statement.

National security offences carry a maximum sentence of life in prison.

The publisher will appear in court on Saturday in relation to the national security charge, police said.

Lai is the owner of Hong Kong's best-selling Apple Daily, a popular tabloid that is unashamedly pro-democracy and fiercely critical of authorities.

Police raided the newspaper's headquarters in August and arrested a string of senior company figures, including Lai, on suspicion of "collusion with foreign forces" under the vaguely worded new law that Beijing imposed on Hong Kong.

Last week he was denied bail and remanded into custody until April after being charged with fraud, the latest in a string of prosecutions brought against high-profile democracy campaigners.

He is set to apply for bail on that charge at the High Court on Tuesday.

London expressed alarm after Lai was charged and said it had raised his case with the authorities.

"The UK remains deeply concerned about the Hong Kong authorities' focus on pursuing legal cases against pro-democracy figures like Jimmy Lai," who has British citizenship, a spokesman for Prime Minister Boris Johnson told reporters.

China's clampdown on Hong Kong has dramatically accelerated since it imposed the security law in June, with opposition politicians disqualified from the legislature and dozens of activists charged or investigated.

Last week three prominent young democracy campaigners -- including Joshua Wong -- were jailed for taking part in last year's democracy protests.

On Friday Hong Kong teenager Tony Chung was found guilty of insulting China's national flag and unlawful assembly.

The 19-year-old, who led a now-disbanded pro-democracy group, was convicted for throwing the Chinese flag to the ground during scuffles outside Hong Kong's legislature in May 2019.

Lai is only the fourth person charged under the controversial national security legislation.

The others are a 19-year-old activist for allegedly promoting secession on social media, a man who rode his motorbike into police officers at a protest and a man who repeatedly shouted pro-democracy slogans at police.

Hong Kong media mogul Jimmy Lai will appear in court on Saturday in relation to the national security charge, police said
Hong Kong media mogul Jimmy Lai will appear in court on Saturday in relation to the national security charge, police said AFP / ISAAC LAWRENCE

During the police operation on Apple Daily, journalists streamed dramatic footage on Facebook as police raided its offices and led Lai away in handcuffs.

The newspaper's front page showed him being detained with the headline "Apple will fight on".

In Chinese state media he is routinely cast as a traitor, "black hand" and anti-China "rabble-rouser".

Lai has long said he fears authorities want to shutter his newspaper and had vowed to use the outlet to continue speaking out against Beijing.

"I'm prepared for prison," Lai told AFP in an interview two weeks before the security law was imposed.

"I'm a troublemaker. I came here with nothing, the freedom of this place has given me everything. Maybe it's time I paid back for that freedom by fighting for it," he added.

The entrepreneur was born in mainland China but moved to the former British colony at age 12.

Prosecutors have tried bringing cases against him in the past.

He was acquitted in September of intimidating a reporter from a rival pro-government newspaper.

The corruption watchdog also dropped a case against him over political donations to pro-democracy supporters after four years of investigations.

Authorities deny targeting Apple Daily or Lai and say police are simply enforcing breaches of the law.

The crackdown has provoked outrage in the West and fear for millions who last year took to the streets to protest against communist China's tightening grip on the semi-autonomous city.

After introducing the law in June, Beijing says stability and order have been restored and has dismissed the huge crowds that protested as a foreign plot to destabilise China.

Critics say Beijing has shredded the freedoms and autonomy Hong Kong was promised ahead of its handover by Britain in 1997.