A 14-year-old teenage boy has been shot, becoming the second victim of gunfire in the latest series of violent protests to hit the streets of the Chinese-ruled city of Hong Kong.

The ABC reported police spokesperson Yolanda Yu said a police officer fired a single shot from his gun in self-defence after he was attacked by protesters in the northern Yuen Long district on Friday night.

She said a male was wounded, but that police did not know exactly how he got shot.

Footage filmed by Hong Kong media company Apple Daily showed a plain-clothes police officer being pinned to the ground by protesters after a gunshot was heard.

According to Apple Daily, he was suspected of having bumped into a person & was surrounded by protesters. [He] shot a young person in the left thigh. He was then beaten by protesters, before a petrol bomb was hurled at him. The officer dropped a magazine as he escaped from fire. https://t.co/GC2bcZcv2I

— Yenni Kwok (@yennikwok) October 4, 2019

A hospital spokesman said the teenager was in a serious but not critical condition, the ABC reported.

The teenage boy is the second victim of alleged police violence on the streets of Hong Kong. On Tuesday, during China’s National Day celebrations, Tsang Chi-kin, 18, was shot by police at close range.

He has since been charged with rioting and attacking police.

The government said Mr Tsang’s condition was stable after surgery.

A protester is treated at the scene after being shot in Hong Kong on Tuesday. Photo: Hong Kong Campus TV

The sudden crackdown on face masks has sparked further uprising.

Hong Kong’s chief executive Carry Lam invoked emergency laws not used since the 1960s colonial era, enforcing six months in jail for wearing the public face coverings.

The ban, which went into effect on Saturday, spurred thousands of protesters to hit the streets while two activists filed legal challenges on the grounds it would instill fear and curtail freedom of speech.

Defiant masked protesters rampaged as police fired tear gas. They crammed streets in the central business district and other areas, shouting “Hong Kong people, resist!”

Face masks have become a hallmark of protesters in Hong Kong amid fears of retribution or having their identities shared with China.

Some young protesters also wear full gas masks and goggles to protect against tear gas.

Masked protesters outside the UK’s Hong Kong embassy call on Britain to stand with them against China’s domination. Photo: Hong Kong Free Press 

Ms Lam invoked the rarely used emergency powers to quell four months of anti-government demonstrations.

Ms Lam said the mask ban would be “an effective deterrent to radical behaviour”.

“We must save Hong Kong – the present Hong Kong and the future Hong Kong,” she said.

“We must stop the violence … we can’t just leave the situation to get worse and worse.”

Ms Lam said she would seek the legislature’s backing for the ban later. She insisted the semi-autonomous Chinese territory was not in a state of emergency but wouldn’t rule out a further toughening of measures if violence continued.

She dismissed suggestions that she should resign, saying it would be unhelpful at a time when Hong Kong is in “a very critical state of public danger”.

Hong Kong leader Carrie Lam has used the city’s Emergency Regulations Ordinances, a rule that grants her the ability to bypass the legislature and make any law during a time of emergency or public danger. Photo: Getty

Pockets of angry protesters attacked Chinese bank outlets and shops, vandalised subway stations and set street fires, prompting police to respond with tear gas in many areas.

Ms Lam’s ban applies to all public gatherings, both unauthorised and those approved by police.

It makes the wearing of any face coverings, including face paint, punishable by one year in jail.

A six-month jail term could be imposed on people who refuse a police officer’s order to remove a face covering for identification.

Masks will be permitted when wearers can prove they need them for work, health or religious reasons.

-with AAP