The demonstrations started in Hong Kong since June and since then no instance of police resorting to firing had been reported so far.

The violence escalated late on Sunday evening when a smaller group of protesters broke away from the day's main march and proceeded onto an extended march that had not been approved. They used traffic cones and street railings to build makeshift barricades in the street, and threw bricks and petrol bombs, CNN reported.

In videos that have gone viral on social media, a policeman could be seen pointing a gun towards the sky.

In a few other videos, the protesters could be seen attacking the policemen with sticks.

In another first instance, Sunday night also witnessed police personnel deploying water cannon against protesters earlier during the day.

Police deployed tear gas into the group but failed to disperse them, and later used a water cannon against a makeshift barricade. This is the first time water cannons have been used in a protest in the past three months, a Hong Kong police spokesperson tells CNN.

"Having given repeated warnings to the protestors in vain, the anti-riot Police officers have deployed tear gas and used minimum respective force to disperse protestors. The Police appeal to everyone on site to leave immediately and condemn all violent acts by the protestors," the police tweeted.

Hong Kong has been witnessing protests over a controversial extradition bill.

The bill would have enabled extraditions to mainland China.

Hong Kong has witnessed anti-government and pro-democracy protests in recent times.

Protests also took place at Hong Kong International Airport which had disrupted flight movement recently.