Hong Kong police will hold an inquiry to determine whether it was appropriate for an officer to fire two warning shots during unrest in Mong Kok.
Two handgun shots were fired into the air as hundreds of people clashed with police on Monday night.
The unrest began when officials began an operation to clear out unlicensed street food stalls.
More than 90 people, mostly police officers and reporters, were injured and dozens of people were arrested.
Protesters threw bricks and bottles at police, who were using batons and pepper spray.
Despite the attempted crackdown, food stalls were operating as usual again on Tuesday evening.
Mong Kok clashes
What happened in Mong Kok?
Hong Kong police attempted to shut down unlicensed food stalls along the junction of Shan Tung Road and Portland Street in Kowloon. Clashes erupted after dozens of local activists gathered to defend the vendors.
The unlicensed food stalls were set up for the Lunar New Year holiday. Officials usually turn a blind eye to the hawkers' lack of official permits, but this year decided to crack down.
Were the clashes just about street food?
The underlying tensions go deeper. Many "localist" groups, who want greater autonomy for Hong Kong, turned up to support the vendors, arguing that Hong Kong's identity is under threat. Trust between the public and the police has also declined in recent years. On social media the protest was dubbed #fishballrevolution, after one of the snacks on sale.
Read more: More than fishballs
Video footage showed one officer firing into the air after police and protesters rushed into the middle of the street, and one officer was tackled by a protester.
Police Commissioner Stephen Lo announced the inquiry at a press conference on Tuesday, but defended the officer who fired the shots.
"Rioters attacked a police officer with hard objects and threatened his life. He fell on the ground but kept being attacked by the rioters.
"With no alternative, his police colleague used his firearm in accordance with the use of force principles, to prevent his fellow colleague from being further attacked and also for his own personal safety," he said.
However some people have accused the police of using excessive force in breaking up the protests.
One reporter for the Ming Pao newspaper has said he is filing an official complaint against police, alleging he was attacked by a police officer.
Officials say they are also investigating whether the trouble was organised in advance.
It was the largest unrest in Hong Kong since massive pro-democracy street protests were held in 2014, although BBC correspondents said the Mong Kok clashes appeared more violent than those in 2014, which were largely peaceful.