HONG KONG (AFP) — Chaos engulfed Hong Kong’s financial heart on Saturday night as police fired tear gas and water cannon 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 on Friday arrested several key activists and legislators in a dragnet on pro-democracy figures.

But on Saturday afternoon, tens of thousands of protesters — many in their signature black T-shirts and under a colourful canopy of umbrellas — defied the order to march on Hong Kong island chanting “reclaim Hong Kong, revolution of our times”.

As evening fell, violence ricocheted through the city’s commercial centre, with a minority of hardcore protesters unleashing a barrage of petrol bombs and rocks at riot police.

Thick, black smoke swirled from a large fire started by masked demonstrators at a barricade on a major thoroughfare, moments from Hong Kong police headquarters. The fire was extinguished after burning for around half an hour.

Earlier police fired a water cannon and rounds of tear gas to disperse protesters massed in front of the city’s parliament, known as the Legislative Council (LegCo), which was stormed in July during the early days of the protest movement.

The crowd briefly broke through the barrier outside the building, but were repelled by tear gas and jets of blue-coloured liquid fired from the water cannon.

Local media reported that the blue spray aimed to make it easier to identify suspects.

“Peaceful protest doesn’t work,” 22-year-old demonstrator Stone told AFP, giving one name.

“I think they (the hardcore protesters) have to vent their anger to achieve something.”

As protesters streamed away, graffiti on a pillar inside a nearby metro station read: “We shall never surrender.”

“Radical protesters” threw “corrosives and petrol bombs” at officers, Hong Kong police said in a statement, posing a “serious threat” to everyone at the scene.

Earlier on Saturday, protesters marched by the official residence of Hong Kong’s embattled Beijing-backed leader Carrie Lam, who is the focal point of anger after trying to pass a bill which would have allowed extradition to China.

Opposition to the extradition bill — now suspended but not permanently withdrawn — has brought much of Hong Kong to the streets, with millions marching peacefully but also groups of radical protesters clashing with police.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 push 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.

Many demonstrators are determined not to let the new movement fizzle out like the Umbrella protests did.

“It’s ‘now or never’ for Hong Kong,” said a 33-year-old accountant who gave her surname as Wong.

“I’m a mother-of-two. They didn’t come today but their grandmother did. We’re defending the right of assembly for the next generation in Hong Kong.”

At least five high-profile activists and three lawmakers were arrested on Friday in a sweep aimed at defanging Saturday’s rally.

Rights groups say the tactics are cribbed directly from Beijing’s protest playbook.

Two of the Umbrella Movement’s leaders, Joshua Wong and Agnes Chow were among those arrested, charged and bailed for “inciting others to take part in unauthorized assembly”.