Hong Kong pro-democracy activist and media tycoon Jimmy Lai has been charged under the city's national security law, amid a widening crackdown on dissent, according to local media reports.

Lai, who founded the Apple Daily tabloid, was charged on suspicion of colluding with foreign forces and endangering national security, local broadcaster TVB reported Friday.

He is the most high-profile person to be charged under the law since it was implemented in June.

Police said in a statement that they arrested a 73-year-old man under the national security law, but did not name him.

Lai was arrested under the national security law in August.

He and two executives of Next Digital, the company that operates the Apple Daily newspaper, were later charged for fraud over accusations that they violated lease terms on office space the company. He was denied bail earlier this month.