Police, who were expecting a backlash, were not seen at many flash points for hours as radical protesters went on the rampage.

Police began taking control later at night, firing tear gas at violent mobs on both sides of the harbour, from Wong Tai Sin, Tuen Mun and Tsuen Wan to Causeway Bay and Aberdeen.

Protesters set a Bank of China branch on fire in Tsuen Wan. Photo: Winson WongRioting anti-government protesters paralysed large swathes of Hong Kong with wanton destruction on Friday, hours after the city’s leader announced that a law against wearing masks would be imposed at midnight.

They vandalised and burned shops, bank outlets and metro stations, forced the closure of the city’s entire railway network and blocked roads, wearing masks in open defiance of the new law.

Police, who were expecting a backlash, were not seen at many flash points for hours as radical protesters went on the rampage.

Police began taking control later at night, firing tear gas at violent mobs on both sides of the harbour, from Wong Tai Sin, Tuen Mun and Tsuen Wan to Causeway Bay and Aberdeen.

Even as Chief Executive Carrie Lam Cheng Yuet-ngor announced the ban from government headquarters at Tamar in the afternoon, the chaos was brewing just blocks away.

Around 1,000 protesters, many of them office workers in suits and pupils in school uniform, gathered on Pedder Street in Central shortly after 4.30pm.

They were soon joined by more, and similar protests began mushrooming across the city, causing traffic chaos.

The protesters built barricades on Man Yiu Street outside the Hong Kong MTR station, stopped traffic on Connaught Road Central and Des Voeux Road Central, and burned a national flag and giant red banner celebrating the 70th anniversary of the founding of the People’s Republic of China on a bridge connecting Jardine House and Chater House.

Among the now familiar plethora of slogans, a new refrain was taken up: “No crime masking our face, no reason to enact the law.”

As night fell, the anarchy intensified and spread.

Police said an officer had opened fire with live ammunition when he was attacked by protesters in Yuen Long. Video footage posted online showed the officer, in a white T-shirt, being beaten by a mob and dropping a drawn gun as he was hit by a petrol bomb. The officer grabbed the gun back from a protester who picked it up in the chaos.

A 14-year-old boy suffered a gunshot wound in the leg just before the incident but there was no official confirmation of a link.

Rioters ramped up their sustained campaign of destruction against the city’s rail operator, having accused it of colluding with the police force to close down stations.

In Kwun Tong, Sha Tin and Sha Tin Wai MTR stations, they destroyed turnstiles, smashed advertisement billboards and daubed graffiti on the walls and ticket machines. A train was seen with its roof on fire in Sha Tin, and in Shek Mun a water hydrant was set off, flooding the station.

As the night wore on, huge fires were lit at entrances of Causeway Bay, Mong Kok and Tsuen Wan MTR stations.

By 10.30pm, they had forced the closure of every MTR station in an unprecedented shutdown of the entire railway network.

Shops and banks with links to mainland China were also targeted by rioters. They smashed the glass facade of a Bank of China branch in Tsuen Wan and threw petrol bombs inside.

ATMs were smashed or set alight in Mong Kok and other areas.

In Central, they smashed shop windows of MX, a food chain owned by Maxim’s. Its founder’s daughter, Annie Wu, infuriated protesters last month by calling them rioters and saying they did not represent Hong Kong.

Another mob set paper and cardboard alight outside the Chinese General Chamber of Commerce offices, while other protesters broke the gates at a branch of China Travel Service in Sha Tin.

Earlier in the afternoon at Chater Garden, Central, Tim Wong Kwok-wai, a 25-year-old marketing officer, said Lam’s move would inflame passions and provoke greater unrest in the city.

“Just as Carrie Lam has held the first dialogue session with the public, she is now bringing forward the anti-mask law, shattering any trust and foundation for further talks,” he said.

Banker Joe Wu, 30, said he was more worried about what the law would lead to.

“Peaceful protesters will still come out, just not wearing masks, if masks are banned. And police are already arresting everybody else on the streets, who may be just shouting at them, so it doesn’t make much difference,” he said.

“But I am deeply concerned about the next step. What evil law will the government introduce next, after opening the floodgate of emergency powers? They can do anything.”

Additional reporting by Sum Lok-kei and Linda Lew