Hong Kong censors are to vet all films for national security breaches under expanded powers announced on Friday, in the latest blow to the financial hub's political and artistic freedoms.

Authorities in semi-autonomous Hong Kong have embarked on a sweeping crackdown to root out Beijing's critics after huge and often violent democracy protests convulsed the city in 2019.

Hong Kong has boasted a thriving film scene and for much of the latter half of the last century, Cantonese cinema was world class Hong Kong has boasted a thriving film scene and for much of the latter half of the last century, Cantonese cinema was world class Photo: AFP / VIVEK PRAKASH

A new China-imposed security law and an official campaign dubbed "Patriots rule Hong Kong" has since criminalised much dissent and strangled the democracy movement.

The latest target is films.

Hong Kong still maintains some key studios, a handful of lauded directors and a thriving indie scene Hong Kong still maintains some key studios, a handful of lauded directors and a thriving indie scene Photo: AFP / VIVEK PRAKASH

In a statement on Friday, the government said the Film Censorship Ordinance had been expanded to include "any act or activity which may amount to an offence endangering national security".

"When considering a film as a whole and its effect on the viewers, the censor should have regard to his duties to prevent and suppress acts or activities endangering national security, and the common responsibility of the people of Hong Kong to safeguard the sovereignty, unification and territorial integrity of the People's Republic of China," the new guidance, which is effective immediately, states.

Slick mainland Chinese and South Korean blockbusters have come to dominate the regional film scene Slick mainland Chinese and South Korean blockbusters have come to dominate the regional film scene Photo: AFP / Ed Jones

Films are rigorously vetted on the Chinese mainland and only a handful of Western films or documentaries ever see a commercial release each year.

Hong Kong's Film Censorship Authority has traditionally employed a much lighter touch.

Historically, the city has boasted a thriving film scene and for much of the latter half of the last century, Cantonese cinema was world-class.

Key points of China's recently imposed national security law for Hong Kong. Key points of China's recently imposed national security law for Hong Kong. Photo: AFP / John SAEKI

In more recent decades, slick mainland Chinese and South Korean blockbusters have come to dominate the regional film scene.

But Hong Kong still maintains some key studios, a handful of lauded directors and a thriving indie scene.

Yet there are growing signs authorities want to see an increase in mainland-style controls over the cultural and art scenes in Hong Kong.

Over the past week, health officials have conducted spot checks on a protest-themed museum and a separate exhibition, stating neither have the correct licenses. The museum had been operating for years without issue.

In March, an award-winning documentary about Hong Kong's massive pro-democracy protests was pulled hours before its first commercial screening after days of criticism from a pro-Beijing newspaper.

It said the film's content breached the new national security law.

Earlier this year a university cancelled a prestigious press photography exhibition that featured pictures of the 2019 protests, citing security concerns.

And M+, a multi-million-dollar contemporary art museum expected to open soon, has said it will allow security officials to vet its collection for any security law breaches before it opens to the public later this year.

A government spokesperson said film censors would strike a "balance between protection of individual rights and freedoms on the one hand, and the protection of legitimate societal interests on the other".