HONG KONG - Hong Kong Police Force has strict guidelines regarding the use of firearms and all officers are required to justify their enforcement actions, the city's police said in a statement as it rejected online rumors that frontline officers were ordered to use their firearms recklessly in Monday's operations.

Such rumors surfaced after a police officer shot a man in a clash with protesters at Sai Wan Ho in eastern Hong Kong Island on Monday morning.

In the statement, police said that owing to radicals' extensive illegal acts, officers responded with dispersal and arrest operations. During such operations, one police officer discharged his service revolver and one male was shot, police said.

An online video footage showed that at an intersection near a Mass Transit Railway (MTR) station in Sai Wan Ho, a police officer fired a shot when he was trying to subdue a protester but was surrounded by several black-clad men.

Hong Kong's Hospital Authority said a man injured in the incident was sent to hospital.

In Sha Tin and Tung Chung operations, officers drew their service arms from their holsters, police said in the statement.

"We appeal to radical protesters to be calm and rational. Protesters should stop all acts that threaten other people's safety and obstruct police's lawful execution of duty," police said.

According to local news reports, the 21-year-old man shot by police in Sai Wan Ho is in hospital and remains in critical condition.

At a routine press conference later in the day, police said the traffic officer who opened fire in Sai Wan Ho this morning was trying to disperse the mob and clear a barricade blocking the road outside Tai On Building. When he was subsequently surrounded by several rioters, the officer pulled out his revolver as a warning.

Ignoring his warning, a man wearing white shirt grabbed him from behind. As they struggled, a man wearing a black shirt attempted to snatch away the revolver at which point the officer opened fire.

"At that time, the officer believed it is very likely the revolver would be snatched and the consequence would be disastrous," said police spokesman Jon Tse Chun-chung.

The spokesman said the officer fired three shots, including the one that hit the man.

He said the matter was being investigated by the force's regional crime unit of Hong Kong Island and police would scan closed-circuit television (CCTV) footages and online videos to conduct an in-depth probe.

At the press conference, the spokesman decried the leakage of personal data of the police officer who opened fire. He said the officer received death threats online targeting his children.