HONG KONG — On a Hong Kong street corner, a young protester found himself staring at the end of an angry police officer’s handgun. He was shot.
Across town on an overpass, a middle-aged man argued with rowdy protesters, accusing them of lacking patriotism for the Chinese motherland. He was set on fire.
By nightfall, both were in the hospital, fighting for their lives.
The actions on Monday were the violent expressions of a city on edge and seething with resentment. The protesters are furious with a police force they see as acting with impunity, while their detractors are angry with the increasingly destructive demonstrations.
Months of antigovernment protests have thrown the Chinese territory into its worst political crisis in decades, with no end in sight. The movement, which started as a fight over an extradition bill, has morphed into a broader call for democracy and police accountability in the former British colony. But neither side seems to agree on what the future should look like under Chinese rule — and neither seems willing to compromise.
Carrie Lam, the city’s embattled chief executive, denounced the unrest on Monday, saying the escalating violence would not force the government to give in to the protesters’ demands. She called those who had set the man on fire “enemies of the people.”
Tensions had been building for days, following the death of a student last week who fell from a parking garage amid demonstrations. The protesters see him as a martyr, and have depicted his death as another sign of excessive police violence.
In response, they called for the city to join in a strike on Monday, disrupting transit en masse and messing up the morning commute. Events across the city, including classes at most of its universities, were canceled.
Monday’s unrest was ugly from the outset. The police officer drew a handgun on the protester as commuters, snarled by roadblocks set up by demonstrators, looked on in disbelief. Several shots rang out, and the 21-year-old man crumpled to the ground in the middle of an eerily deserted intersection.
As blood pooled on the asphalt, a crowd of angry pedestrians surrounded riot police officers who had arrived as reinforcements. “Murderer!” some of them cried, while an officer doused the crowd with pepper spray.
Anger over the shooting quickly unspooled across several districts in the city of more than seven million people, drawing suit-clad office workers in the central business district and residents in working-class neighborhoods.
The scale of the transit disruptions on Monday was not as large as a citywide strike that protesters staged on a weekday in early August. Yet the clashes between protesters and the police were intense by any measure; the shooting was only the third time the police have shot a protester since the demonstrations began in June.
Notably, some clashes occurred on the fringes of leafy university campuses that have in recent months generally been off limits to such violence. Protesters threw Molotov cocktails and glass bottles at police lines, while officers responded by firing tear gas and rubber bullets.
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Thousands of black-clad protesters also turned up for a flash mob-style demonstration in Hong Kong’s central business district around lunchtime, creating a starkly surreal aura in an area filled with luxury malls. Some front-liners used orange traffic cones, bricks and wooden poles to set up barricades on main roads.
On the side of a Giorgio Armani store, a screen with a video ad that showed sleek models parading down a runway was defaced with graffiti: “They shoot, they murder, they are well-paid.” And protesters, some of them office workers in full face masks, yelled insults at police officers along the same lines.
“Shooting everywhere, you think you’re so cool?” one asked an officer at one point, adding an expletive. “Have you killed someone yet today? Have you met your killing quota?”
Marcus Lee, a 26-year-old lawyer in a charcoal gray suit with a blue face mask, stood outside with a group of protesters who were shouting at the police.
“The gun wasn’t necessary, let alone firing shots,” he said, referring to the morning’s shooting. “You can see how people are reacting to this. They are angry. It’s just very ridiculous.”
Scattershot violence erupted throughout the city for much of the day.
Video footage showed a police officer on a motorcycle in the Kwai Fong district of northern Hong Kong swerving into a crowd of protesters, clipping at least one of them. The police later said the officer had been suspended from front-line duties.
Across town in Ma On Shan, a district near the border with the Chinese mainland, a video showed a man who appeared to be a government supporter being doused with flammable liquid and set on fire after arguing with a group of protesters.
“Go back to the Greater Bay Area!” the protesters shouted at him, using Beijing’s term for the region of southern China that includes Hong Kong and neighboring cities.
As many Hong Kong residents prepared for their evening commute, the smell of tear gas lingered outside their office buildings. In an internal memo, the bank HSBC said that while it was still operating normally, its employees should “leave the office early and under safe conditions.”
The Hospital Authority said that both the protester who had been shot and the man who had been set on fire were in critical condition.
On Monday afternoon, the police urged protesters to stop threatening public safety. The authorities said that the officer who fired the three live rounds in the Sai Wan Ho area had acted in self-defense against protesters who had been trying to steal his revolver.
“We certainly believe our officer did not have bad intention to hurt anyone,” John Tse, a top police official, told reporters.
Mrs. Lam, the city’s leader, called Monday’s mayhem “destructive” and said it could “take Hong Kong to the road of ruin.”
“The behaviors of these rioters have already far exceeded this so-called fight for demands,” Mrs. Lam said, describing those who were responsible for the man’s burning.
Mrs. Lam also made it clear that the government would not be pressured into making concessions to the protesters, describing such expectations as “wishful thinking.”
“I am making this statement clear and loud here,” she said. “That will not happen.”
Katherine Li, Ezra Cheung and Paul Mozur contributed reporting.