Firing live rounds during Tuesday's chaos was lawful and necessary as the police officer faced a life-threatening situation, Hong Kong's legal professionals and police experts said on Wednesday.

They made the comments after a police officer shot and wounded an 18-year-old pipe-wielding protester in self-defense and to protect his colleagues on Tuesday afternoon in Tsuen Wan, the New Territories, amid violent protests on National Day. It is the first time a live bullet has hit a rioter since Hong Kong's social unrest began in mid-June.

According to online video clips, the officer was besieged and attacked by 10 rioters wielding hammers and iron rods — one even speared him with a sharpened stick.

At a police media briefing on Wednesday, Tang Ping-keung, deputy commissioner of police, stressed that firing a shot is in line with Hong Kong Police Force guidelines and international standards.

"What we are talking about is whether the measure can effectively stop protesters," said Wong Wai-shun, senior superintendent of the Operations Bureau.

At the time, other close-range, non-lethal weapons — such as pepper spray — would not be enough to contain the situation, especially when outnumbered by a riotous mob.

Some critics questioned the officer's decision to fire at such a short distance. But Lawrence Ma Yan-kwok, a barrister and chairman of the Hong Kong Legal Exchange Foundation, backed the police officer.

As the attacker was too close to the officer, the officer had to make an immediate reaction to protect his safety and that of his colleagues, Ma explained.

There has also been some controversy over the police officer's decision to shoot at the protester's body instead of his arms or legs, which may result in less serious injuries.

Ma, also a member of the Independent Police Complaints Council between 2011 and 2016, said there is an internationally accepted principle that police officers must fire the gun at the main body of a perpetrator rather than his or her hands or feet, because it is easier to shoot the target to curb violence quickly.

According to the Article 29 of the Police General Orders, an officer may discharge a firearm when the officer's intention is to protect any person, including himself, from death or serious bodily injury or to effect the arrest of any person who he has reason to believe has just committed a serious and violent crime and who attempts to evade such arrest.

After watching several videos related to the incident, Executive Councilor and barrister Ronny Tong Ka-wah believes there is little possibility the officer had been wilfully assaulting the protester as he performed his duty in accordance with police protocol in such urgent circumstances. There is no proof of any criminality in this case, Tong said.

In a video recording the scene, the protester was seen attacking the police officer with a steel pipe which hit the officer's revolver-holding arm and touched off the shot that wounded the man.

If the police officer did not shoot the protester and his pistol dropped after the demonstrator hit his arm, the consequences might have been disastrous, Tong noted.

The lives of he and his colleagues were under serious threat, and he abided by the Police General Orders, Deputy Commissioner Tang said. "We have never had such an order or instruction as ‘shoot to kill', or to ‘assault to kill'," he added.

On Tuesday, the Hong Kong Police Force arrested 269 people on charges including possession of offensive weapons and unlawful assault.