Thousands of people took to the streets of Hong Kong for the second consecutive day Sunday, many wearing face masks in defiance of a new anti-mask law that protesters fear could open the floodgates to more draconian rules.

The black-clad demonstrators marched peacefully in the rain on both Hong Kong Island and the Kowloon Peninsula in the unauthorized protest against the regulation, which went into effect Saturday.

"Hong Kong people, resist!" the crowd chanted. "Fight for Freedom! Stand with Hong Kong!"

Police fired tear gas and other weapons to disperse the crowds, who after the march protest set up roadblocks with barricades and umbrellas on roads near the police headquarters in Admiralty and a police station in Prince Edward. A water cannon truck was also deployed to clear the crowd.

Protesters threw petrol bombs at the police headquarters, from where police fired rounds of tear gas in return. As the protesters retreated eastward toward Wan Chai district, the police continued to push forward and fired tear gas on a major street lined with residential and commercial buildings.

By invoking the colonial-era Emergency Regulations Ordinance on Friday, Chief Executive Carrie Lam and her Cabinet enacted the Prohibition on Face Covering Regulation to tackle what she described as an "extremely violent situation" and to "bring calm back" to Hong Kong in light of the ongoing protests, triggered by a now-suspended extradition law.

"It's not just the anti-mask law, but the emergency ordinance, which allows the government to do whatever it wants," said a 23-year-old woman who identified herself by her initials I.I. "(The mask ban) is just the first, next to come will definitely be a ban on insulting police or other draconian laws."

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Since the protests started in June, many protesters have worn surgical masks or air-filtering masks at public gatherings to protect themselves from tear gas and pepper spray used by police and to maintain anonymity.

The new law, which will be tabled for discussion in the legislature after it went into effect, carries a maximum penalty of one-year imprisonment and a fine of HK$25,000 ($3,200). Failure to remove a mask at the request of police could result in a six-month jail term and fine of HK$10,000.

Attempts to ask the court to suspend the law until it is decided whether a judicial review will proceed were quashed.

Local media reported that 13 people have been arrested for violating the new law.

"The chief executive has run out of moves and could only resort to draconian measures," said a 45-year-old man surnamed Lai. "Infiltrating the rioters to make chaos and use the chaos to justify the need to invoke emergency power and ban face masks, what's next? Suppression only yields resistance."

Mass protests have continued despite the government's announcement last month that the extradition bill will be formally withdrawn in October.

The protesters' demands have widened to include an independent inquiry into police use of violent tactics against demonstrators, pardons for all those arrested and democratic reform.

In continuation from Saturday, about half of the subway system, some banks and shops and major malls were shuttered to prevent damage by protesters, who have targeted the subway and shops run by Chinese companies.

Chaos was reported in various districts across the territory by nightfall.

At least three individuals who were seen arguing with some protesters were attacked in Kowloon, but police were nowhere to be seen.

Some protesters shined lights at the Chinese army barracks in the Kowloon Tong district, according to the local newspaper Ming Pao Daily.

In response, a few solders on a rooftop in the barracks raised a flag warning the protesters to stop and also pointed high-power flashlights back at them, the report said. The crowd left as police arrived on the scene later.

By nightfall, a large group of protesters remained in Kowloon's Mong Kok district after police fired tear gas at them and left.