HONG KONG -- Hong Kong officials invoked sweeping emergency powers that would ban the wearing of masks by protesters during demonstrations.
Carrie Lam, the city's chief executive, on Friday announced the invocation of the colonial-era Emergency Regulations Ordinance. The law's authority is to be used for the first time since 1967, and the mask ban will take effect from midnight.
"Public order is at a very dangerous state, and violence is destroying Hong Kong," Lam told reporters in the city. "It's not an easy decision, but it's a necessary move under the current situation."
Late Friday, flash mobs appeared all across the city, playing a cat-and-mouse game with riot police. As officers closed in, large groups of protesters retreated to new areas in an effort to stay one step ahead. Those scenes played out continually through the night.
Local media reported that the entire MTR rail system was shut down out of safety concerns.
Meanwhile, hard-line demonstrators continued to vandalize properties and businesses with mainland China connections or perceived leanings to Beijing.
Lam said that she was not "100% sure that this single step that we have taken" would achieve the government's objective to end the violence. If conditions continue to deteriorate, "then as a responsible government we will continue to have to identify other means that will tackle the situation."
Emergency authority allows the chief executive to lawfully censor media, take control of private properties, and suspend business activities, among other powers.
Lam said she believes the law could create a deterrent effect against violent protesters, and that it is aimed to restore order in society and make it easier for police to identify anyone violating the law.
But she stressed that imposing the anti-mask law under the emergency ordinance does not mean that Hong Kong will be entering a state of emergency.
Protesters use high-tech masks to protect themselves from tear gas fired by police and to hide their identities. Images of protesters donning highly sophisticated face masks have become commonplace since June.
The new law would apply to all protests -- lawful and unlawful. Anyone wearing anything, including face paint, to hide their faces at approved rallies with more than 50 people or at authorized marches with more than 30 participants would be breaking the law. Violators would face up to a year in prison or a fine of HK$25,000 ($3,190).
People who cover their faces for professional, medical or religious purposes are exempt. The exemption includes journalists.
Protesters began gathering in the Central business district -- home to international companies and major banks -- after the announcement, blocking roads and setting fires on the street.
Earlier, thousands of people in face masks marched through the district during the lunch hour to protest against the ban. Office workers and others voiced support for the protesters' five demands on the government, only one of which has been met: the withdrawal of a controversial extradition bill.
Beijing said it supported the Lam's move. Yang Guang, spokesperson for China's Hong Kong and Macao Affairs Office of the State Council, said the situation in Hong Kong could not continue indefinitely, Reuters reported. Yang repeated China's previous claims that the protests were evolving into a revolution with foreign intervention, the report said.
Lam said that she and other top government officials will continue their dialogue with the public. The first such session -- a tense meeting between the chief executive and more than 100 members of the community -- took place last week but failed to appease pro-democracy activists.
Pro-democracy lawmakers and others denounced the invocation of the emergency powers, saying they would effectively end Hong Kong's "one country, two systems" legal framework that has been in effect since the 1997 handover.
The Civil Human Rights Front, which has organized several peaceful marches since June, strongly criticized the government's decision, which bypasses debate in the city's main lawmaking body, the Legislative Council.
"This old, severe colonial law must be abandoned to keep the government in check and stop it from persecuting Hong Kong residents," the group said in a statement.
With the introduction of emergency powers, "Hong Kong is now a colony under Mainland Chinese rule," it said.
Joshua Wong, the student leader of the 2014 Umbrella Movement, said Friday's decision would allow the government "to do whatever it wants."
"It is a de facto Martial Law, with no PLA marching on the streets, but would bring an equivalent threat of violence to the city," Wong said in a tweet.
Paris Tse, a 41-year-old unemployed resident, said he would continue to wear masks to future rallies.
"We will not accept such a law," said Tse, wearing a black mask, as he headed to a rally on Friday evening after Lam's announcement. "I think the government just wants to suppress protests."
Also Friday, the government said that the Legislative Council would resume sessions on Oct. 16 and that the extradition bill, opposition to which sparked the protests, would be formally withdrawn "immediately after" Chief Executive Carrie Lam delivers her annual policy address, public broadcaster RTHK reported.
Stocks in Hong Kong traded lower on Friday, with the Hang Seng Index closing down 1.1% after the announcement was made.
Financial Secretary Paul Chan said the law would not hurt Hong Kong's competitiveness, adding that the city has a stable economic system and would continue to attract foreign investment.
He also said that the government would not impose controls on foreign exchange, which would violate the principles of the Basic Law, Hong Kong's mini-constitution.
MTR, the operator of the city's railway system, on Friday warned protesters to stop damaging stations amid escalating vandalism targeted at the company, which is majority-owned by the government.
Protesters use the efficiency of the city's transport network to move quickly around the city, but also have caused damage and set fires at stations.
More than 120 stations out of a total 161 across the city have been deliberately damaged by protesters, including roughly 800 turnstiles and 500 ticketing machines, MTR Operations Director Adi Lau Tin-shing said at a news conference.
"We can see from recent incidents the amount of equipment damaged has been escalating," Lau said. He said of even greater concern was protesters throwing petrol bombs into stations "and setting fire to our station entrances and throwing objects onto tracks and overhead lines."
Contributing writer Olivia Tam in Hong Kong contributed to this article.