Several water cannon trucks firing blue water have been stationed around Hong Kong as police attempt to identify protesters.
Teargas and coloured blue water has been fired dramatically from a water cannon truck at raging protesters who threw gasoline bombs at government headquarters in Hong Kong.
Demonstrators were doused by the high-pressure coloured water after taking over roads and major intersections in popular shopping districts as they rallie.
Local media reported that the coloured spray aimed to make it easier to identify suspects.
Authorities closed streets and a subway station near the Chinese government office and parked water cannon trucks and erected additional barriers nearby, fearing protesters might target the building.
The mostly young protesters, in their signature black T-shirts and masks, marched in the Causeway Bay shopping district, with the crowds beginning to grow after dusk.
The stand-off continued for some time, but protesters started moving back as word spread police were headed in their direction.
Frontline protesters hurled gasoline bombs at the officers in formation.
"Peaceful protest doesn't work," 22-year-old protestor Stone told AFP, giving one name.
"I think they (the hardcore protesters) have to vent their anger to achieve something."
Streets were set aflame as demonstrators targeted a roadblock near Hong Kong police headquarters, sending plumes of black smoke into the night sky.
The scenes seem certain to inflame tensions in a city driven by nearly three months of pro-democracy demonstrations.
Later that night police stormed an underground railway carriage and hit passengers with batons and pepper spray.
Police were swinging batons at passengers on the platform of Prince Edward subway station as they backed into one end of a train car shielding themselves with umbrellas.
Police say they entered the station to arrest offenders after it was believed protesters assaulted others and damaged property.
It wasn't clear if all the passengers were protesters.
Angry crowds gathered outside Prince Edward and nearby Mongkok station, where police said they made arrests after protesters vandalised the customer service centre and damaged ticked machines.
Video footage of what unfolded at the station has been widely shared on social media as another example of police brutality during the protests.
It came as police fired tear gas and water cannons at petrol bomb-throwing protesters, who defied a ban on rallying — and mounting threats from China — to take to the streets for a 13th straight weekend.
Police had banned the demonstration on security grounds and arrested several key activists and legislators in a dragnet on pro-democracy figures.
Opposition to the extradition bill — now suspended but not permanently withdrawn — has brought much of Hong Kong to the streets, with millions marching peacefully but also groups of radical protesters clashing with police.
The protests have expanded into a wider pro-democracy call and a rejection of attempts by Beijing to curtail the freedoms of the semi-autonomous territory.
Protesters were in defiant mood throughout Saturday, which marked the fifth anniversary of Beijing's rejection of a call for universal suffrage for Hong Kong that sparked the 79-day "Umbrella Movement" in 2014.