Hong Kong authorities on Friday announced they had frozen the assets of billionaire pro-democracy tycoon Jimmy Lai, including his shares in his media publications, for breaching the city's national security law.

The security bureau said it had issued an order to freeze Lai's shares in Next Digital media group and "the property in the local bank accounts of three companies owned by him".

A rags to riches billionaire, media tycoon Lai has long been a thorn in Beijing's side thanks to his caustic tabloids and unapologetic support for democracy.

His Apple Daily newspaper has staunchly backed Hong Kong's pro-democracy cause, including the huge and often violent protests that swept the international financial hub in 2019.

Lai, 73, was detained last year under a sweeping national security law that Beijing imposed on Hong Kong in a bid to stamp out those protests.

He was charged with "colluding with foreign forces" for allegedly advocating for foreign sanctions against Hong Kong and China's leaders.

He was also convicted and jailed last month for taking part in the 2019 protests.

AFP