Hong Kong's police union on Monday urged officers in the field to use lethal force against violent protesters who threaten their lives.

The recommendation came in a statement by the Junior Police Officers' Association following an outbreak of violence Sunday night in which petrol bombs were thrown by anti-government protesters.

(Pro-democracy protesters react as police fire water canon at them outside the Central Government Complex on Sept. 15, 2019 in Hong Kong.)[Getty/Kyodo]

Since large-scale protests against a now-suspended extradition bill erupted in June, the police have been using teargas and other "non-lethal" weapons such as beanbag rounds, rubber bullets and water cannon against violent protesters.

"I must remind the radical rioters that the petrol bombs you use are deadly weapons," association chairman Lam Chi-wai said in the statement.

He cited an incident in which two traffic officers patrolling on bikes were ambushed by protesters who hurled petrol bombs at them, forcing the duo to unholster their firearms to disperse the crowd.

"Whenever rioters prepare to hurl petrol bombs, officers on the field could very likely interpret that as a life-threatening attack against themselves or others and respond with relevant use of force or weapons, including firearms with real bullets," he said.

Lam said the association urges members to act decisively on the use of force or weapons when lives are under threat. According to the police code, the level of force used could be one level higher than that used by opponents.

A mostly peaceful march on Hong Kong Island on Sunday turned violent as it concluded in the evening, when protesters hurled bricks and petrol bombs at police guarding the government headquarters in Admiralty.

Water cannons were used to disperse demonstrators who defied teargas fired by police. As they retreated, the protesters vandalized two subway stations nearby. The protesters accuse the subway operator of aligning with the authorities.

(A protester hurls a petrol bomb at the government headquarters in Hong Kong on Sept. 15, 2019.)

Violent clashes subsequently spread to other districts throughout the night between protesters and pro-government supporters who opposed them, with the fiercest outbreaks occurring in the North Point area.

At least 28 people were injured, according to the Hospital Authority, including 11 men who remain hospitalized.

In an internal notice, the police commissioner, Stephen Lo, condemned the increasingly violent demonstrations, consoled the officers on the hardship they face and vowed full support to help them finish the task.

"Hong Kong police is the main law enforcement force of Hong Kong and its last line of defense. Irrelevant of the situation, the police will continue our hard work in restoring social order and lead Hong Kong back on the right track," he said.

Hong Kong leader Carrie Lam's recent decision to formally withdraw the contentious extradition bill failed to appease the protesters, whose demands also include pardons for all those arrested and democratic reform.