China has said the lack of tough security laws in Hong Kong is a key reason for months of increasingly violent pro-democracy demonstrations and that the enactment of such legislation is an "urgent task".

The call -- likely to further inflame protesters angry with a police response seen as heavy-handed -- came in a lengthy statement issued late Saturday by the head of the Chinese government department that oversees Hong Kong.

The statement by Zhang Xiaoming, director of the Hong Kong and Macau Affairs Office, acknowledged that governance in the semi-autonomous city must be improved, saying factors such as high housing costs and a growing wealth gap had contributed to the unrest.

But Zhang also backed a firmer hand, saying laws outlawing subversion and other challenges to Chinese central government control were needed, and stressed that the territory's leader and legislature must be "patriots" loyal to Beijing.

Efforts by Hong Kong's Beijing-controlled government to introduce tough security laws in 2003 caused major protests before being shelved.

The lack of such legislation "is one of the main reasons for the intensification of activities of local radical separatist forces", Zhang said.

"The need to safeguard national security and strengthen law enforcement have become prominent issues and urgent tasks facing the government of the Hong Kong Special Administrative Region and people from all walks of life."

Zhang's statement will likely further enrage Hong Kong protesters who have upended the international finance hub with their movement.

Chinese President Xi Jinping last week expressed a "high degree of trust" in Hong Kong's unpopular Chief Executive Carrie Lam, following speculation that Beijing was preparing to remove her.

Hong Kong has been shaken by months of increasingly violent pro-democracy protests
Hong Kong has been shaken by months of increasingly violent pro-democracy protests AFP / Nicolas ASFOURI

While giving no indication that her removal was imminent, Zhang said: "It must be ensured that the Chief Executive is a patriot trusted by the central government (who) loves one's country and Hong Kong."

The city's "administrative, legislative and judicial organs also must be composed mainly of patriots".

Hong Kong's legislature is quasi-democratic, with half the seats popularly elected and the rest chosen by largely pro-Beijing committees, ensuring it remains stacked with government loyalists.

The lack of fully free elections -- especially the fact that the city's leader is appointed by a pro-Beijing committee -- has fuelled years of protests culminating in the latest unrest.

Hong Kong holds district council elections on November 24, with the pro-Beijing camp bracing for heavy defeats.

Since the protests kicked off, voter registration has soared and the pro-democracy camp is fielding candidates in every constituency for the first time.

But there are concerns the elections could be called off due to the violence.

On Wednesday, one of the city's most stridently pro-Beijing politicians was wounded in a knife attack by a man who pretended to be a supporter.

That assault came three days after a Mandarin-speaking man shouting pro-Beijing slogans knifed at least three pro-democracy protesters and bit off the ear of a local district councillor.