Hong Kong police have charged two executives from the pro-democracy Apple Daily newspaper using a powerful new security law, a day after the company's newsroom was raided over articles it had published.

Police said a 47-year-old and a 59-year-old were charged with "collusion with a foreign country or with external elements to endanger national security".

Apple Daily said the two charged executives were chief editor Ryan Law and CEO Cheung Kim-hung.

Some 500 officers descended on the paper's newsroom yesterday, bundling computers and notepads into evidence bags.

Authorities said the operation was sparked by articles that allegedly appealed for sanctions against China.

It was the first time articles published in Hong Kong have sparked arrests under the new law that cracks down on dissent in the international business and media hub.

Five Apple Daily executives were arrested in the operation.

Police said the remaining three were still in custody and being questioned. The two charged executives would appear in court tomorrow, Saturday.

Over 100 people have been arrested under the new security law which China imposed on Hong Kong nearly a year ago to stamp out dissent in the wake of huge pro-democracy protests.

More than 60 have been charged and the vast majority have been denied bail.

Five convicted over mob attack on Hong Kong protesters

Five men who took part in a mob attack on Hong Kong democracy supporters two years ago have been found guilty of rioting and wounding in the first convictions over an assault which sparked widespread outrage.

The attack took place in the train station of Yuen Long - a town close to the rural border with mainland China -- during huge democracy rallies that were convulsing the finance hub.

Dozens of men dressed in white and wielding sticks pounced on protesters returning from a rally in the city, as well as reporters and ordinary commuters, sending some 50 people to hospital.

Live broadcasts of the attack, and the police's perceived failure to respond quickly enough, was a turning point in the huge protests, further hammering public trust in the city's government.

A district court judge today convicted five attackers.

He said merchant Tang Wai-sum, driver Ng Wai-nam, rural leader Tang Ying-bun and electrician Choi Lap-ki were "principal offenders" in the attack.

A fifth defendant, electrician Wong Ying-kit, "encouraged the white-clad men to assault others".

A sixth defendant, transport worker Wong Chi-wing, was acquitted after the judge ruled he could not be clearly identified in the CCTV footage.

All five offenders, together with two other defendants who previously pleaded guilty, will be sentenced on 22 July, one day after the second anniversary of the attack.

The attack was a public relations disaster for Hong Kong's police force, especially after officers were photographed talking to men in white wielding sticks and letting them leave the scene.

Only a tiny fraction of the Yuen Long attackers were arrested.

Local media have reported many slipped across the border to mainland China.

Police have confirmed some of those involved in the attack have links to triad organised crime gangs.

More recently, senior police officers have sought to recast the attack as a pitched battle between two evenly matched sides.

Police arrested some of those who were on the receiving end of the attack, including former opposition lawmaker Lam Cheuk-ting who was badly beaten.

Mr Lam is expected to go on trial in 2023, charged with rioting.