1119 GMT February 23, 2020
Chief Executive Carrie Lam said she had made the order under the Emergency Regulations Ordinances, a sweeping provision that grants her the ability to bypass the legislature and make any law during a time of emergency or public danger, AFP reported.
"We believe that the new law will create a deterrent effect against masked violent protesters and rioters, and will assist the police in its law enforcement," Lam said.
But as soon as the law was announced, masked demonstrators built barricades in the heart of Hong Kong's commercial district and began holding flash-mob rallies in multiple districts.
The largest impromptu rally on Friday broke out in central Hong Kong, where many blue-chip international firms are based, as thousands of protesters blocked roads, erected barricades and built street fires.
Critics said the move was a major step towards authoritarianism for Hong Kong, which has been governed by China under a "one country, two systems" framework since British colonial rule ended in 1997.
Prominent democracy activist Joshua Wong said the law "marks the beginning of the end of Hong Kong".
The last time the law was invoked was during the 1967 riots – a period where more than 50 people were killed in a year-long leftist bombing and murder spree.
Hong Kong's protests were ignited by a now-scrapped plan to allow extraditions to the mainland.
Protesters have used face masks to avoid identification and respirators to protect themselves from tear gas.
The ban came after Hong Kong was rocked by the worst violence of the year on Tuesday, the same day China celebrated 70 years of Communist Party rule.