Flash-mob rallies broke out in Hong Kong on Wednesday as anger mounted over police shooting a teenage protester who attacked officers in a dramatic escalation of the violent unrest that has engulfed the territory for months.

Large crowds of demonstrators held unsanctioned marches through the commercial centre and then in multiple districts throughout the evening, when police fired brief volleys of tear gas in one neighbourhood, chanting anti-police and anti-government slogans.

Hundreds of students also staged a sit-in at the school of Tsang Chi-kin, 18, who was shot in the chest by a policeman as he and a group of masked protesters assaulted officers with umbrellas and poles.

Tuesday witnessed the worst clashes of the summer as China celebrate 70 years of Communist Party rule with a massive military parade in Beijing.

The spiralling violence underscored seething public anger against Beijing’s rule and shifted the spotlight from China’s carefully choreographed birthday party.

Running battles raged for hours across multiple locations as hardcore protesters hurled rocks and petrol bombs. Police responded for the most part with tear gas, rubber bullets, and water cannon.

As criticism rose, police launched a spirited defence of their colleague saying he feared for his life and the safety of his colleagues. “He only had one option, that is to fire the gun to immediately resolve the danger,” deputy commissioner Tang Ping-keung told reporters on Wednesday.

The Junior Police Officer’s Association also called on authorities to use colonial-era emergency regulations and impose a curfew as it launched a stinging attack on the city’s pro-Beijing leaders.“The police force has been fighting alone,” JPOA chairman Lam Chi-wai said, lamenting the lack of a political solution to the chaos.

Opinion towards Tuesday’s shooting has largely cemented along ideological divides with pro-democracy activists condemning the police and establishment figures calling it a justified use of force.

Protest groups said the officer charged into the melee with his firearm drawn and failed to fire a warning shot as they condemned the increasing use of live rounds.