Carrie Lam announced that the use of face masks at "illegal" and "unauthorized" protests will constitute as unlawful under the new regulation, which comes into effect at midnight, Deutsche Welle reports.
Anyone breaching the law could face up to one year in prison and a fine of up to 25,000 Hong Kong dollars (US $3,200, €2905) if they fail to adhere to the new rules.
Lam said that Hong Kong "isn't in a state emergency" but faces "extensive and very serious danger" after a surge in violent protests across the city. "We must stop the violence ... Now, it's all over Hong Kong."
Lam said that the mask ban targeted violent protests and rioters and "will be an effective deterrent to radical behavior." Lam was expected to go to the legislature to obtain legal backing for the rule.
Pro-democracy protesters marched through Hong Kong's city center on Friday ahead of Lam's conference on deploying emergency powers to ban people from wearing face masks at public rallies.