China's plans to impose a new security law on Hong Kong will "only target a handful of lawbreakers", the city's leader said Tuesday, as she tried to reassure international businesses and investors rattled by the proposal.

Beijing wants to enact legislation banning "seccession, subversion, terrorism and foreign interference" in the international finance hub after months of massive, often-violent pro-democracy protests last year.

Many Hong Kongers, business groups and Western nations fear the proposal could be a death blow to the city's treasured freedoms and usher in an end to the semi-autonomous city passing its own laws.

The announcement of plans for the new law -- which will be written by Beijing and bypass Hong Kong's legislature -- sparked the biggest drop on the city's stock exchange in five years on Friday.

But Carrie Lam said fears the city's business-friendly freedoms were at risk were "totally groundless".

"Hong Kong's freedoms will be preserved and Hong Kong's vibrancy and the core values in terms of the rule of law, the independence of the judiciary, the various rights and freedoms enjoyed by people, will continue to be there," Lam told reporters.

The proposed law, she added, "only targets a handful of law-breakers... it protects the vast majority of law-abiding, peace-loving residents".

Hong Kong was upended last year by seven months of huge and often violent pro-democracy protests, sparked by years of rising fears that Beijing is chipping away at the city's freedoms.

Millions took to the streets for rallies that routinely ended with clashes between riot police and smaller groups of militant protesters wielding petrol bombs.

Security law imposition plans spark protests
Plans to impose a security law sparked new protests in Hong Kong over the weekend. Photo: AFP / Yan ZHAO

Beijing portrays the protests as a foreign-backed plot to destabilise the motherland and has justified the security law as a way to crack down on "terrorism" and calls for independence.

Protesters say their rallies are the only way to voice opposition in a city with no universal suffrage.

Thousands of protesters took to the streets on Sunday after the security law announcement and were dispersed by tear gas and water cannon in the worst clashes in months.

The precise wording of the security law has yet to be revealed but China's rubber stamp parliament previewed initial details last week.

It is expected to approve a draft of the law on Thursday and analysts say it could be implemented some time in the summer.

Of particular concern is a provision allowing Chinese security agents to operate in Hong Kong, with fears it could spark a crackdown on those voicing dissent against China's communist rulers.

Subversion laws are routinely wielded against critics on the mainland.

Asked by a reporter whether mainland police would be able to arrest protesters in Hong Kong, Lam dismissed the question as "your imagination".

She said anti-government protests would continue to be allowed "if it is done in a legal way" but did not elaborate on what views would be considered illegal under the new law.

Copyright AFP. All rights reserved.