Carrie Lam, Hong Kong's chief executive, speaks during a news conference in Hong Kong, China, on Friday, Oct. 4, 2019. Kyle Lam | Bloomberg | Getty Images

Hong Kong leader Carrie Lam on Friday invoked emergency powers and banned face masks, saying the order goes into effect Saturday. Consequences for breaking the ban include up to one year in jail and a fine of 25,000 Hong Kong dollars ($3,187). Violators must be prosecuted within a year of the date on which the prohibition was broken, according to a copy of the ban. In a press conference, Lam said the face mask ban was necessary because "almost all protesters who carry out vandalism and violence covered their face." "The purpose was to hide their identity and evade the law and they have become more and more daring," Lam said. The ban also empowers police to ask people in public places to remove items covering their face in order to identify them. It also allows officers to remove the covering if the person does not comply. Failing to remove a mask when a police officer asks carries a fine of 10,000 Hong Kong dollars ($1,275) and up to six months in jail. She noted, however, that the mask ban contains certain exemptions "to cater for legitimate needs." @cnbcSri: #BREAKING: Hong Kong gov't announces legislation to ban face masks at public gatherings under section 2 of the Emergency Regulations Ordinance. Handout obtained by @CNBCi at gov't press briefing. #HongKongProtests Surgical masks have become ubiquitous in the city after the 2003 outbreak of SARS, a disease that killed 298 people in Hong Kong, according to World Health Organization data. Protesters often wear gas masks to protect themselves from tear gas fired by police. Others wear bandanas, surgical masks or even Guy Fawkes masks to conceal their identities at peaceful demonstrations. Hong Kong's parliamentary body, the Legislative Council, will discuss the legislation on Oct. 16 when it resumes session, Lam said.

Pro-democracy demonstrators march from Chater Garden during a protest against a potential government ban on protesters wearing face masks in Hong Kong on October 4, 2019. Nicolas Asfouri | AFP | Getty Images

The Hong Kong leader said the decision was made after she called a special meeting of the Executive Council, which decided to invoke the Emergency Regulations Ordinance. Lam said the government believes the regulation will have a "deterrent effect" against violent behavior and help police officers carry out their duties. Under the 1922 law, the chief executive is allowed to "make any regulations whatsoever which he may consider desirable in the public interest." It also states that any regulations drafted under this ordinance will remain in place until repealed by the chief executive. Hong Kong has been swallowed by mass demonstrations since early June. Protest initially began over a now-withdrawn bill that would have allowed extradition of criminal suspects to mainland China.

Tensions at new highs

Lam's comments come after tensions hit a new high on Tuesday, China's National Day, after an 18-year-old anti-government protester was shot by police, the first person hit by live gunfire in nearly four months of unrest. The protester has been charged with rioting and attacking a police officer. Local authorities have repeatedly said the officer fired his weapon in self-defense. Multiple videos of the shooting show protesters carrying objects like wrenches and hammers.

Protester returns a teargas canister during the demonstration. Ivan Abreu, SOPA Images | LightRocket | Getty Images

Of the roughly 1,100 people injured in the protests, Lam said at least 300 were police officers. "There's a use of lethal weapons, corrosive liquids, snatching of suspects and snatching of police pistols. So, the police have no choice but to use their guns to save their own lives," Lam said. According to Reuters, police in the Chinese territory were given greater power to use force during protests, ahead of China's 70th National Day last Tuesday. Reuters reported that officers fired approximately 1,400 rounds of tear gas and nearly 900 rubber bullets. The city is a former British colony and returned to Chinese rule in 1997. As a special administrative region of China, Hong Kong operates under a "one country, two systems" structure, which grants its residents legal and economic freedoms that citizens in mainland China do not have.

Colonial-era law

But it isn't immediately clear whether Lam's use of emergency powers under a colonial-era law is legal. "It's questionable, highly questionable, whether this is even constitutional," David Webb, former director of Hong Kong Exchanges and Clearing, told CNBC on Friday, before the law was invoked. "If the government can make laws on its own, then you'll be heading down a slippery slope because they can next pass laws blocking parts of the internet, or allowing detention without trial, for example, and all laws without any Legislative Council scrutiny," he added.