Police officers have pulled their guns and reportedly shot a warning shot at protesters in Hong Kong after being attacked with sticks and rods.
Crowds have taken to the streets for a second day in a row following a pro-democracy march.
Public broadcaster RTHK says one of its reporters saw a uniformed officer fire a shot into the sky over the heads of protesters, as tension between police and protesters rumbles on.
The confrontations were the latest violence in a summer of protests that have shaken the city's government and residents.
Police fired teargas to disperse the crowd and they also brought out water cannon trucks for the first time in the summer-long protests, although they were not used directly at protesters.
Demonstrators have responded by throwing bricks and petrol bombs towards the police.
Large crowds gathered in a park and hard-line protesters took over a main street of the semi-autonomous Chinese territory, strewing bamboo poles on the pavement and lining up orange and white traffic barriers and cones to obstruct the police.
Some protesters said they are resorting to violence because the government has not responded to their peaceful demonstrations.
"The escalation you're seeing now is just a product of our government's indifference toward the people of Hong Kong," said Rory Wong, who was at the clash after the march.
Prior to the skirmishes, tens of thousands of umbrella-carrying protesters marched in the rain in Hong Kong's latest pro-democracy demonstration.
People were chanting "Fight for freedom, stand with Hong Kong" at a post-march rally in Tsuen Wan Park, the South China Morning Post newspaper said.
The march started near the Kwai Fong railway station, which has become a focal point for protesters after police used tear gas in the station earlier this month - the first time tear gas has been fired inside.
Protesters have taken to the streets for more than two months, initially in reaction to an proposed extradition bill which would have seen suspected criminals extradited to mainland Chinese to face trial.
However the legislation has since been suspended but the demonstrators' demands have morphed into a broader call for democratic elections, an investigation into police use of force to quell the protests and for the city's leader Carrie Lam to step down.
The clashes, while not as prolonged or violent as some earlier ones, ended a brief lull in the violence.
The protests had been largely peaceful the previous weekend, after weeks of escalating violence.
Police said they arrested 29 people, ranging from 17 to 52 years old, for various offences, including unlawful assembly, possession of offensive weapons and assaulting police officers.