From Friday midnight, face masks are banned at “unlawful” and “unauthorised” protests in Hong Kong, Chief Executive Carrie Lam said at a media conference.
Any protester defying the ban could be jailed up to one year and fined $3,187.
The rule does not apply to those covering their faces because of medical, religious or professional reasons.
The ban comes after Hong Kong witnessed violent protests on Tuesday as China celebrated 70 years of Communist Party rule with a rally showing its military might.
The local administration imposed the mask ban evoking colonial-era Emergency Regulations Ordinance which protesters called unconstitutional.
Lam said Hong Kong is not in a state of emergency although the administration has evoked the emergency regulation.
She defended the mask ban saying public order was under threat from student protesters who had vandalised public property.
Lam did not rule out tougher measures under the emergency provisions if the violence worsened.
As soon as Lam’s announced the ban, masked protesters staged impromptu rallies across Hong Kong’s districts chanting they want to wear face masks and wearing them is not a crime.
They attacked public property, stopped the railway network and blocked roads. Although police anticipated a backlash against the mask ban, they were deployed too late in sensitive points.
As rioting intensified around midnight, an officer opened fire on protesters in self-defence in Yuen Long. A 14-year-old protester was injured in the leg in the firing.
A video footage shows the officer being beaten by protesters over a traffic incident. He drops the gun as a petrol bomb hits him. When a rioter picks up the gun, the officer snatches it from his hands.
Pro-democracy activist and the young face of 2014 Umbrella Revolution, Joshua Wong, said the mask ban is as harmful as the extradition bill which sparked the weekend protests on June 9.
The emergency ban marks the beginning of the end of Hong Kong as more bans could be coming, he said.
Protesters and journalists covering weekend rallies have been wearing masks to conceal their identity or protect themselves from tear gas and pepper spray used by police to disperse crowds.
While Lam believes the mask ban will deter people from joining weekend protests, it may lead to bigger rallies.
Many wonder how the ban can be enforced when over a million protesters take to the streets.
Teenage students have been leading the unprecedented weekend protests most of which were unlawful as the local administration did not give approval to them.
The youths are so inspired by democracy and freedom that they ignore the government’s warning of 10-year jail term.
On Tuesday, a teenager was critically injured in police firing while he was attacking a police officer with an umbrella and pole.