Police fired water cannon and tear gas in running battles with brick-throwing anti-government protesters in Hong Kong on Sunday, the second day of violent clashes in the Chinese-ruled city.

The protesters, many in masks and wearing black, threw several petrol bombs, some taking off down narrow side streets in the pouring rain. Water cannon have never been used until now in years of anti-government protests.

The MTR rail operator had suspended some services to try to prevent people gathering. But tens of thousands of protesters, calling for democracy for the former British colony, made it to a sports stadium in the vast container port of Kwai Chung, from where they marched to nearby Tsuen Wan.

Some dug up bricks from the pavement and wheeled them away to use as missiles, others sprayed detergent on the road to make it slippery for the lines of the police. Clashes spread in many directions as protesters broke shopfront windows and threw tear gas canisters back at the police.

The vast majority marched peacefully as a large contingent of protesters split up, radiating out to at least four other locations across Hong Kong to launch smaller, wildcat demonstrations that the police sought to disperse, sometimes with tear gas.

There was a sense of chaos across swathes of the Kowloon peninsula, over the harbour from the main island of Hong Kong, with police sirens blaring, tear gas wafting throughout densely populated areas.

The clashes on Saturday and Sunday marked a return to unrest after days of calmer demonstrations. The protests, which started in June over a now-suspended extradition bill, have rocked Hong Kong for three months, occasionally causing serious disruption including unrest at the airport.

Traffic was blocked on Nathan Road, which heads south to the key harbourside tourist area of Tsim Sha Tsui. Protesters temporarily blocked off the northern Kowloon-side end of the oldest harbour tunnel, smashing toll booths.

The police in Tsuen Wan had warned earlier they would launch a “dispersal operation” and told people to leave.

Hundreds of protesters remained long after nightfall, discussing what to do next, surrounded by empty tear gas canisters, bricks, metal railings and other debris.

Some “radical protesters” removed railings and set up barricades with water-filled barriers, bamboo scaffolding, traffic cones and other objects, the police said in a statement.

One policeman fired a pistol shot into the air, the police told media. There was no response from the police on whether it was a live round.

Activists threw petrol bombs and bricks on Saturday in the gritty industrial district of Kwun Tong, on the east of the Kowloon peninsula.

The city, a major Asian financial centre, is facing its biggest political crisis since the handover of power from British rule in 1997. Protesters say they are fighting the erosion of the“one country, two systems” arrangement under which Hong Kong returned to China with the promise of continued freedoms, not enjoyed on the mainland, for 50 years.