Hong Kong police shot and wounded a teenage boy on Friday, as violent protests erupted across the Chinese-ruled city hours after its embattled leader Carrie Lam invoked colonial-era emergency powers last used more than 50 years ago.

Lam, speaking at a news conference, said a ban on face masks would take effect on Saturday under the emergency laws that allow authorities to “make any regulations whatsoever” in whatever they deem to be in the public interest.

Nearly four months of anti-government protests have plunged Hong Kong into its biggest political crisis since its handover from Britain to China in 1997 under a “one country, two systems” formula that granted it autonomy and broad freedoms not enjoyed on the mainland.

The Beijing-backed leader said the banning of face masks was necessary to quell escalating violence and didn’t rule out the prospect of further measures if the unrest continued.

Sirens echoed through the streets as protesters set fires, hurled petrol bombs at police and burned the Chinese national flag, in a direct challenge to authorities in Beijing.

Police said an officer in Yuen Long, a district in the outlying New Territories that saw fierce clashes in July, had fired a shot in self-defense after a protester threw a petrol bomb at him, setting him on fire.

Local media reported a 14-year-old boy had been shot and the city’s Hospital Authority said a 14-year-old was in a serious condition, without giving further details.

Around a hundred demonstrators besieged a Bank of China (HK) branch in the high-end shopping district of Causeway Bay, while across the harbor in Kowloon district protesters smashed the glass store front of a China Life branch.

Police fired volleys of tear gas to disperse protesters in flashpoint districts across the territory, including Causeway Bay, Sha Tin and Wong Tai Sin, underscoring the challenges facing authorities as the protests show no sign of letting up.

“COLOR REVOLUTION”

China’s Hong Kong and Macao Affairs Office praised Lam’s move in a statement that said the protests were evolving into a “color revolution”, a term coined to refer to popular uprisings in Ukraine and other former Soviet states that swept away long-standing rulers, with interference from external forces.

The emergency laws allow curfews, censorship of the media, and control of harbors, ports and transport, although Lam did not specify any particular action that might follow beyond the mask ban.