HONG KONG — This major financial hub and usually vibrant city of 7 million was reduced to confusion and quiet Saturday morning, as Hong Kong woke to find its entire subway system shut down, buses disrupted, and supermarkets and malls shuttered in anticipation of more protests.

The semiautonomous Chinese territory is on edge after Hong Kong leader Carrie Lam announced she would invoke rarely used emergency powers to ban masks at protests, a decision that immediately intensified anger and unrest on city streets. On Friday night, a peaceful march through the city spiraled into pockets of riots as protesters torched subway stations and businesses linked to pro-Beijing tycoons.

Glass shards remained scattered across pavements the next day from shops that had been vandalized, with their windows smashed. MTR Corp., which operates the city’s rail network, said it had to shut the entire network after “the outbreak of violence at multiple districts” to ensure the safety of its staff. The unprecedented move was in effect for all of Saturday. 

Even always-reliable 7-Eleven convenience stores would be closed at 5 p.m., the chain announced on its Facebook page.

“This is the really one very sad day for Hong Kong,” said Dennis Kwok, a pro-democracy lawmaker who represents the legal sector.

Kwok filed an urgent legal challenge to the mask law along with 23 other pro-democracy lawmakers on Saturday, seeking a judicial review of the law as well as a temporary injunction. A hearing is set for Sunday morning.

“The reason why the people were out there protesting against the extradition bill is because they feared that their freedoms will be taken away,” he said. “Now, [the government has] demonstrated that the fears are justified, that the Hong Kong government will do anything to take away the rights and freedoms of Hong Kong people.”

Among the nearly three dozen people hospitalized in the protests Friday night was a 14-year-old boy, shot in the left thigh by an undercover police officer. After he fired at the boy, a group threw a petrol bomb at the officer, briefly setting him on fire. 

The police force characterized the shooting as justified, as did Lam, who addressed the city in a five-minute pretaped video released on Saturday afternoon. As she spoke in the recorded tape, speaking of “unprecedented” levels of vandalism and destruction on Friday night, she was flanked by more than a dozen of her ministers.

“Fellow citizens, the extreme acts of the rioters brought dark hours to Hong Kong last night and half paralyzed society today,” Lam said. “Everyone is worried, anxious and even in fear. The [Hong Kong government] will curb the violence with the greatest determination.”

Protesters on Saturday morning debated on Web forums and secure messaging apps the merits of “taking a rest” amid the city shutdown, but others did not want to deliver the government a victory after the new government restriction. By 3 p.m., a few hundred people had begun marching peacefully from the shopping district of Causeway Bay. Later in the day, others linked hands in a vigil in the Tsim Sha Tsui area along Victoria Harbor and marched through Kowloon neighborhoods. 

Most of the protesters were still wearing surgical masks to cover their faces. 

The effect of stronger police enforcement could already be felt. In central Hong Kong, riot police tackled a young man and his girlfriend, both of whom were wearing masks, in front of the iconic HSBC headquarters building in central Hong Kong. Several officers in full riot gear, backed by about 40 of their colleagues nearby, pinned them to a divider at a tram stop while they searched through their bags. Passersby heckled the officers and told them to leave.

The man and his girlfriend were not arrested. The man, speaking to The Washington Post after officers had left, said he didn’t understand what he had done wrong. His girlfriend was in tears. He spoke on the condition of anonymity because of privacy issues. 

The government’s decision to implement the mask ban and the use of emergency powers to do so came at a time of already heightened emotions in the city, after an 18-year-old boy was shot in the chest by police in one of several chaotic protests in the city on Tuesday — the 70th anniversary of the People’s Republic of China. The emergency powers, which date back to Hong Kong’s time under British colonial rule in 1922, were last used during leftist riots in 1967, which left more than 50 dead.

Critics have accused Hong Kong’s government of once again being out of touch with the population, as lawmakers were when they proposed legislation that would allow extradition to mainland China — the spark of the protest movement back in June. Demands have now swelled to include direct elections for Hong Kong and — crucially — an independent investigation of a police force many fear is operating with impunity. 

Tiffany Liang and Timothy McLaughlin contributed to this report.