Hong Kong leader Carrie Lam banned protesters from wearing masks on Friday in a hardening of the government's stance on the territory's most disruptive crisis since it reverted to Chinese rule in 1997. But even before the new rule was confirmed, protests against it began across the Asian financial hub, with hundreds of office workers wearing masks gathering to march. The mask ban, imposed under a colonial-era Emergency Ordinance, takes effect on Saturday. It applies to unauthorised public gatherings and police-approved protests. Large crowds of mostly office workers hit the streets during the workday lunch break over the pro-Beijing regime's expected use of colonial-era laws that opponents said would tip the city towards authoritarianism. Seething public anger against Chinese rule of the semi-autonomous city has exploded into huge demonstrations and increasingly violent confrontations, with no sign of an end to nearly four months of unrest, and activists vowing an 18th consecutive weekend of protests. Protesters have used face masks to avoid identification - along with yellow helmets, goggles and respirators to protect themselves from tear gas and police projectiles. Multiple local media outlets reported embattled leader Carrie Lam had decided to turn to the Emergency Ordinance Regulations to outlaw face coverings and had met her cabinet on Friday morning. The government said Lam and senior cabinet ministers would hold a press conference at 3pm (0700 GMT) But protesters have already vowed to defy the law. "Youngsters are risking their lives, they don't mind being jailed for ten years, so wearing masks is not a problem," a 34-year-old office worker wearing a surgical mask, who gave her first name as Mary, told AFP at a protest on Friday afternoon. The expected ban comes after Hong Kong was rocked by the worst violence on the year on Tuesday, the same day China celebrated 70 years of Communist Party rule. Street battles raged for hours between riot police and hardcore protesters while a teenager who was part of a group that attacked police with umbrellas and poles was shot in the chest with a live round - the first such shooting since the demonstrations began. Protesters have increasingly resorted to hurling bricks and Molotov cocktails while police are firing tear gas and rubber bullets with unprecedented frequency. On Friday the city's subway system said 83 of its 91 underground stations had been vandalised in recent months after protesters turned on the operator because it began shutting down parts of the network ahead of large protests. Pro-establishment lawmakers and a prominent police officer association have ramped up their calls for the government to invoke the emergency laws, which were last used 52 years ago by the British during deadly leftist riots. The law allows the city's leader to make "any regulations whatsoever" in the event of an emergency or public danger without the need to go via the city's parliament. During the 1967 riots - a period where more than 50 people were killed in a year-long leftist bombing and murder spree - the British used the ERO to give police extra powers of arrest and rolled out widespread censorship of the press. Government supporters say emergency powers are needed to combat the increased violence of hardcore protesters. But critics have countered that bypassing the legislature and giving Lam the power to make any law would be a slippery slope for an international finance hub that owes its economic success to its reputation for rule of law and judicial independence. "This is a watershed. This is a Rubicon," pro-democracy lawmaker Claudia Mo told AFP. "And I'm worried this could be just a starter. More draconian bans in the name of law could be lurking around the corner." It is also not clear how a face mask ban would be enforceable. Since a deadly SARS outbreak in 2003, face masks have become ubiquitous in Hong Kong. Even moderate protesters have already shown a willingness to break the law in huge numbers, appearing at unsanctioned rallies in their tens of thousands. Simon Young, a law professor at the University of Hong Kong, said a mask ban might deter some moderates from hitting the streets. "But it could well have the effect of bringing more people out simply because they feel the need to protest against the exercise of executive authority," he told AFP.