HONG KONG — The Hong Kong police clashed again on Saturday with protesters, who took to the streets in the tens of thousands despite an official ban, a day after several high-profile activists and pro-democracy lawmakers were arrested.
As government helicopters hovered above the city, riot police officers used tear gas, pepper spray and water cannons at crowds of protesters who had gathered outside government offices and the headquarters of the Hong Kong legislature. Some of the protesters had thrown gasoline bombs.
The clash near government headquarters was reminiscent of the early days of the protest movement in June, though the political stakes are now far higher after months of unrest and political crisis.
Tensions have been running especially high in Hong Kong for days, partly because Saturday was the fifth anniversary of the day that Beijing announced a plan for limited democracy in the territory. That decision angered many in Hong Kong and triggered months of large-scale protests in 2014, and demonstrators planned to mark the anniversary with an enormous march through the city.
But the police declined to issue a permit for the march, and on Friday — the same day lawmakers and activists were arrested — organizers said they were canceling it out of safety concerns.
Many of the protesters began marching west from the playground toward the home of Carrie Lam, the territory’s deeply unpopular chief executive.
By 3 p.m., throngs of marchers had snarled traffic on several major roads in the pouring rain, as riot police officers blocked roads in the central business district that led uphill toward Mrs. Lam’s residence. Some protesters taunted the officers — who the movement has previously accused of using excessive force and working with criminal gangs — by shouting “trash” and “crooked cops.”
As dusk approached and two government helicopters hovered above Hong Kong Island, a broad swath of the city’s downtown had been brought to a standstill, either by protesters or the makeshift barricades they had built across roads. The tear gas was deployed soon afterward.
Hong Kong’s political crisis, the worst since Britain handed the colony back to China in 1997, was set off by widespread anger over a bill that would allow criminal suspects to be extradited to mainland China for trial. The measure, which critics said could be used to target activists, has been suspended, but not withdrawn as protesters have demanded. Demonstrators’ demands have since expanded to include universal suffrage and an investigation of the police.
The police arrested at least three prominent activists on Friday, including Joshua Wong, a well-known leader of the Umbrella Movement, and Agnes Chow, on unauthorized assembly charges related to a June 21 protest in which thousands of people surrounded the police headquarters.
Three lawmakers from Hong Kong’s pro-democracy legislative minority — Cheng Chung-tai, Au Nok-hin and Jeremy Tam — were also arrested on Friday, on charges related to their participation in the protests this summer. Mr. Au and Mr. Tam were released on bail on Saturday, but it appeared that Mr. Cheng was still being held.
Mr. Wong, meanwhile, was already back on the streets, though subject to a police-imposed 11 p.m. curfew.
“The price I paid is just a small piece of cake” compared to what other protesters have been through, he told reporters.
Vincent Ho, 40, arrived at the Wan Chai playground on Saturday with his wife and their 10-year-old son. He said he had wondered whether it was safe to bring his son, but that they planned to leave before anything dangerous happened.
Mr. Ho, who works at a bank, said measures like the extradition bill would make him question whether he was comfortable having his son grow up in the city.
“Our freedom is being taken away,” he said. “Our system is being destroyed, and without that, it’s not Hong Kong anymore.”
The planned route for the now-canceled Saturday march went from Hong Kong’s central business district to the Chinese government’s local liaison office, as a means of focusing public attention on the five-year anniversary of Beijing’s decision to limit elections.
The liaison office was vandalized by a hard-core group of protesters last month, prompting China to denounce them — and to place a plastic shield around a national crest outside the building, which protesters had spattered with ink.
Street violence has come in fits and starts during this summer’s protests, and life in Hong Kong has otherwise proceeded relatively normally. But there is growing fear among a wide cross-section of Hong Kong society that the violence, which has included a mob attack on protesters, could eventually lead to deaths.
Some protesters have in recent weeks thrown bricks, firebombs and other objects at the police, who as of mid-August had fired more than 1,800 rounds of tear gas, plus rubber bullets and beanbag rounds, to disperse crowds.
Last weekend, the police used water cannon trucks for the first time since the protests began in June, and a few officers drew pistols on protesters, some of whom were charging at them with sticks. One officer fired a warning shot into the air after one of his colleagues fell to the ground.
On Friday night, the Hong Kong news media reported, an off-duty police officer was stabbed during an attack by three masked men in a train station. He remained conscious but suffered bone-deep wounds.
Mrs. Lam, the territory’s chief executive, said on Tuesday that the government was looking into “all laws in Hong Kong — if they can provide a legal means to stop violence and chaos.”
Mrs. Lam was answering a question about whether she was considering use of Hong Kong’s sweeping Emergency Regulations Ordinance, a colonial-era law that grants Hong Kong’s leader broad powers to “make any regulations whatsoever which he may consider desirable in the public interest.” One fear is that the law could be used to justify blocking some of the messaging apps that are popular with protesters.
On Thursday, the Chinese military sent fresh troops to its Hong Kong garrison. Although the military called it a routine rotation, the move fueled speculation that Beijing might be quietly expanding its presence in the territory.
People’s Daily, the main newspaper of the Chinese Communist Party, warned Saturday that Beijing would not stand on the sidelines if the Hong Kong government was overwhelmed by “turmoil.” It likened the protesters to arrogant ants, warning that they stood no chance of prevailing over the central leadership in Beijing.
“We also admonish all forces opposing China and throwing Hong Kong into chaos to by no means misjudge the situation and mistake restraint for weakness,” the newspaper said.