Chief Executive Carrie Lam Cheng Yuet-ngor will hold a special meeting of her de facto cabinet, the Executive Council, to impose the ban, according to the sources.

The city’s legislature will only be able to amend or repeal the legislation after implementation.

If approved, the new law would take effect within a short time, one source said, adding: “There’s no point waiting until next week.”

The colonial-era Emergency Regulations Ordinance, introduced in 1922, grants the city’s leader the authority to “make any regulations whatsoever which he [or she] may consider desirable in the public interest” in case of “emergency or public danger."

Masked anti-government protesters marred China’s National Day celebrations on Tuesday with a violent rampage across Hong Kong, prompting police to fire six live rounds – including one which hit a student in his chest – and arresting 269 people for various offenses, including rioting.

The source said the violence on October 1 made the anti-mask law an urgent matter.

“We cannot wait for the Legislative Council, which will only meet on October 16 at the earliest,” he said.

Since Tuesday, Lam has been facing mounting pressure to invoke the ordinance.

Two of Hong Kong’s largest pro-Beijing parties, the Democratic Alliance for the Betterment and Progress of Hong Kong (DAB), and the Federation of Trade Unions (FTU), as well as the Junior Police Officers’ Association (JPOA), have issued separate statements, urging Lam to adopt measures under the ordinance to better tackle the escalating social unrest.

The DAB has proposed banning people from wearing masks in unlawful protests, while those who take part in lawful protests, or those who need to wear masks on religious or health grounds, should be exempted under the proposed law.

In a statement on Wednesday, the JPOA urged the government to adopt measures under the Emergency Regulations Ordinance, or impose a curfew under the Public Order Ordinance, to empower the thinly stretched force to better tackle the escalating social unrest.

On Thursday, JPOA chairman Lam Chi-wai said he supported the anti-mask law as it would give officers a legal justification for handling masked protesters, although it could be challenging.

“Just like the injunction order imposed in the Hong Kong International Airport and the MTR, it gives police a legal ground to exercise their duties there,” Lam said.

“It would be very irresponsible not to introduce the law just because police might experience difficulties while on duty.”

Speaking on a RTHK radio program on Thursday, Executive Council member Ronny Tong Ka-wah also said if he had a choice, he would choose to invoke the emergency law over imposing a curfew.

“The emergency law is more specific and law-abiding ordinary citizens would not be as affected,” he said.

He also revealed some had called for the government to invoke the emergency powers to allow police to detain those arrested for up to 90 hours, from the current 48 hours, on top of enacting an anti-mask law.

“Under an anti-mask law, the police may have to handle a high number of detainees,” Tong said. “Forty-eight hours may not be adequate time for the police to process them for the legal procedures.”

At least 15 countries in North America or Europe have legislation banning people from wearing masks, including the United States, Canada, Germany and France.

An anti-mask law in the United States can be traced to 1845, when tenant farmers wore disguises to attack law enforcement officials. In 1965, the law in some states was updated to prevent masked gatherings of two or more people, except in the case of masquerade parties.

Canada approved a bill in 2013 to forbid people from covering their faces during a riot or unlawful assembly. The offense carries a maximum sentence of 10 years in jail.

Since the 1970s, various European countries enacted laws banning people from wearing masks to hide their personal identity at public events.

As the full-face veil won by Muslim women became a hot-button issue across Europe over the past decade, France was the first European country to ban burkas, niqabs, balaclavas, hoods and other such items in public places with a law that took effect in 2011. Those who violate the law can be fined up to €150 (US$166).