Hong Kong’s streets have descended into chaos again as protesters set up roadblocks and torched businesses on a main tourist street and police responded with tear gas and a water cannon after an unauthorised pro-democracy rally.

Protesters threw firebombs and took their anger out on shops with mainland Chinese ties as they skirmished late into the evening with riot police, who unleashed numerous tear gas rounds, angering residents and passers-by.

Police had beefed up security measures ahead of the rally, for which they refused to give permission, the latest chapter in the unrest that has disrupted life in the financial hub since early June.

Protesters stand on a barricade
Protesters stand on a barricade (Mark Schiefelbein/AP)

Some 24 people were hurt and treated in hospital, including six with serious injuries, the Hospital Authority said. Police did not give an arrest figure.

As the march set off, protest leaders carried a black banner that read “Five main demands, not one less”, as they pressed their calls for police accountability and political rights in the semi-autonomous Chinese territory.

Supporters sang the protest movement’s anthem, waved colonial and US flags, and held up placards depicting the Chinese flag as a Nazi swastika.

Protesters throw fire bombs
Protesters throw fire bombs (Mark Schiefelbein/AP)

Many protesters wore masks in defiance of a recently introduced ban on face coverings at public gatherings, and handed more out to the crowd.

Some frontline protesters barricaded streets at multiple locations in Kowloon, where the city’s subway operator restricted passenger access.

They tore up paving slabs and scattered them on the road, commandeered plastic safety barriers and unscrewed metal railings to form makeshift roadblocks.

A water cannon truck and armoured car led a column of dozens of police vans up and down Nathan Road, a major artery lined with shops, to spray a stinging blue-dyed liquid as police moved to clear the road of protesters and barricades.

Demonstrators in the Tsim Sha Tsui district
Demonstrators in the Tsim Sha Tsui district (Kin Cheung/AP)

At one point, the water cannon sprayed a handful of people standing outside a mosque. Local broadcaster RTHK reported that the people were guarding the mosque and few protesters were nearby.

The Hong Kong police force said it was an “unintended impact” of its operation to disperse protesters and later sent a representative to meet the mosque’s imam.

As night fell, protesters returned to the streets, setting rubbish alight at road junctions, and wrecking discount grocery shops and a restaurant chain because of what they say is the pro-Beijing ownership of the companies.

They also set fire to ATMs and branches of mainland Chinese banks, setting off sprinklers in at least two, as well as a shop selling products from Chinese smartphone maker Xiaomi.

Protesters set fire to a Xiaomi shop in Nathan Road
Protesters set fire to a Xiaomi shop in Nathan Road (Mark Schiefelbein/AP)

The police used a bomb disposal robot to blow up a cardboard box with protruding wires that they suspected was a bomb.

Organisers said ahead of the march that they wanted to use their right to protest as guaranteed by Hong Kong’s constitution despite the risk of arrest.

On Saturday, Hong Kong police arrested a 22-year-old man on suspicion of stabbing a teenage activist who was distributing leaflets near a wall plastered with pro-democracy messages.

A witness told RTHK that the assailant shouted Hong Kong is “a part of China” and other pro-Beijing messages.

The protest movement sprang out of opposition to a government proposal for an extradition bill that would have sent suspects to mainland China to stand trial, and then ballooned into broader demands for full democracy and an inquiry into alleged police brutality.