Hong Kong Chief Executive Carrie Lam speaking at a press conference in Hong Kong on October 4, 2019 where she announced that an emergency law will be invoked and face masks by protesters will be banned.Mohd Rasfan | AFP | Getty ImagesHong Kong leader Carrie Lam on Friday invoked emergency powers and banned face masks, saying the order goes into effect on Saturday, Oct. 5.In a press conference, Lam explained that 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.She said the decision was made after she called a special meeting of the Executive Council, which decided to invoke the Emergency Regulations Ordinance. Lam explained that the government believes the regulation will have a “deterrent effect” against violent behavior and help police officers carry out their duties.Under the 1922 Emergency Regulations Ordinance, 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 It also states that any regulations drafted under this ordinance remain in place until repealed by the chief executive.Hong Kong has been swallowed by mass demonstrations since early June. Protest initially began over a now-withdrawn bill that would have enabled extradition to mainland China.Tensions at new highs Lam’s comments come after tensions hit a new high on Tuesday, China’s National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 that the officer fired his weapon in self-defense. Multiple videos of the shooting show protesters carrying objects like wrenches and hammers.Of the roughly 1,100 people injured in the protests, Lam said that at least 300 of them 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 on Tuesday. Reuters reported that officers fired approximately 1,400 rounds of tear gas and nearly 900 rubber bullets.Protester returns a teargas canister during the demonstration.Ivan Abreu, SOPA Images | LightRocket | Getty ImagesThe 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 citizens legal and economic freedoms that citizens in mainland China do not have.Colonial-era lawBut 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, the 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.Lam argued that these emergency powers are being used to address the “state of serious public danger.””As a responsible government, we have the duty to use all available means in order to stop the escalating violence and restore calmness in society,” she said.Lam also pointed out that similar versions of this prohibition have been used in other countries. Earlier this year, France banned masks after weeks of violence as a part of the “yellow vest” movement.This is breaking news. Please check back for updates.— CNBC’s Stella Soon contributed to this report.