Shots confirmed fired

After sunrise on Tuesday, fires were still burning from rubbish tipped from trash cans. Around 100 protesters were gathered in the area, some of whom were ripping bricks from the sidewalk to hurl at police.

Officers in riot shields deflected the bricks and at one stage charged the protesters, some who later appeared to be bloodied.

A police spokesman said 54 people had been arrested, ranging in age from 15 to 70, and 90 police personnel were injured. Some of the injured officers had broken bones and head wounds.

Four journalists were also injured.

For several hours, the city's underground rail network, the MTR, avoided the station closest to the disturbance. Mong Kok MTR station re-opened mid-morning local time.

'Police officers attacked'

Addressing reporters Tuesday, Leung said that the protesters' actions -- and the police response -- spoke for themselves.

"I believe the public can see for themselves on TV and (from media) reports the seriousness of the situation," he said. "The police (are) under strict guidelines for the use of force."

He added that other police officers had to take all necessary actions to maintain peace.

"Compared to other major cities in the world, the police has shown the greatest degree of restraint in handling the situation."

He added that a scheduled firework display planned for Tuesday night above the city's harbor would go ahead as planned.

RELATED: "Ten Years": Dark vision of Hong Kong's future proves surprise box office hit

Social media response

During the clashes, hashtag #fishballrevolution quickly gained traction, a reference to the street food the vendors were selling.

Hong Kongers took to social media such as Facebook and Twitter -- which, unlike in Mainland China are not blocked -- sharing images and video of the disturbance.

Images shared included screen shots of TV footage which appeared to show officers pointing their sidearms at civilians.

While most Hong Kong Police officers are armed, gun violence in the city is very rare and officers rarely have call to unholster their weapons.

Other posts showed video of a tense standoff between police in riot gear and protesters, and images of bricks broken up to be thrown at the police.

Backdrop of mistrust

The clashes come at a time of worsening relations between Hong Kong and the central Chinese government, with many concerned about Beijing encroaching on the city's freedoms.

Most recently this has manifest itself in uneasiness surrounding the disappearance of a number of booksellers and publishers who deal with material critical of the Chinese government. Critics insist that the men were illegally spirited out of Hong Kong and Thailand by mainland authorities.

The majority of the protesters in Monday night's were young, although there was no evidence that the disturbance was linked to Hong Kong's Occupy movement.

That 2014 movement, also known as the "Umbrella Revolution" saw tens of thousands of protesters, many of whom were students, taking to Hong Kong's streets -- including in Mong Kok -- for 11 weeks in 2014 to protest what many saw as a declaration denying this semi-autonomous city's freedoms by Beijing. During the early days of the Occupy protests, police were criticized for their heavy-handed approach to the peaceful demonstration.

READ MORE: 'Too terrified to travel': A new normal for Hong Kong's 'Occupy Generation'?