Los Angeles Mayor Karen Bass imposed a curfew for parts of Los Angeles, after protests over immigration enforcement in California roiled the city’s downtown area.

Bass said the curfew will run from 8 p.m. to 6 a.m. local time, and cover roughly a square mile of downtown. She said she expects it to last several days.

“The curfew is a necessary measure to protect lives and safeguard property following several consecutive days of growing unrest throughout the city,” Los Angeles Police Chief Jim McDonnell said at a news briefing announcing the curfew. “Since Saturday, we’ve seen a concerning escalation and unlawful and dangerous behavior.”

McDonnell said arrests have risen each day since Saturday, peaking at nearly 200 people arrested on Tuesday. Of the 197 people arrested Tuesday, 130 were detained near the Metropolitan Detention Center downtown and 67 were arrested after occupying the 101 freeway, McDonnell said.

After the curfew went into effect, the Los Angeles Police Department said on X that multiple groups continued to congregate in the curfew zone and “mass arrests are being initiated.”

The curfew comes after President Trump derided the protesters earlier Tuesday, calling them animals and professional agitators. The president gave his speech standing in front of uniformed Army soldiers, who at times cheered and applauded.

“What you’re witnessing in California is a full-blown assault on peace, on public order and on national sovereignty carried out by rioters bearing foreign flags with the aim of continuing a foreign invasion of our country,” Trump said at Fort Bragg in North Carolina. “We’re not going to let that happen.”

The remarks came one day after U.S. Marines were deployed to the Los Angeles area. About 4,000 National Guard troops have been mobilized as well.

In an address Tuesday night, California Gov. Gavin Newsom railed against Trump for eroding the nation’s democracy and amplifying tensions in Los Angele s. He described Trump’s actions to call in the National Guard and Marines as a “brazen abuse of power” that “inflamed a combustible situation.”

Newsom said that Trump chose to create a culture of fear that has led school children to be afraid of attending their own graduations. “We do not want our streets militarized by our own armed forces,” Newsom said.

Newsom implored residents to protest peacefully and said those who don’t will be held to account. The governor ended by saying that the stability of the country itself is at stake. “Other states are next. Democracy is next,” he said. “Democracy is under assault before our eyes.”

Large protests panning Trump’s immigration policies continued to spread to cities across the country on Tuesday night. In New York, hundreds gathered in Manhattan across from the federal buildings that house immigration operations, while in the Atlanta area demonstrators lined Buford Highway, according to news footage. A large protest popped up at the Colorado State Capitol in Denver, and thousands of people marched in Chicago’s central business district waving flags and signs.

“ICE is continuously deporting people without due process,” said Jay Waxse, a 36-year-old community organizer at the Chicago protest. “If we don’t protest against it, then it’s just going to continue to be accepted.”

Also Tuesday, National Guard troops were accompanying ICE agents on operations to arrest immigrants in L.A., a Defense official confirmed. While the Guard members were authorized to protect federal property and officials, their protection of federal officials during arrests is an expansion of their role during days of protest in the nation’s second-largest city.

Earlier on Tuesday, ICE released a picture showing National Guard members protectively surrounding ICE agents in the middle of an arrest.

“Military troops are providing protection for federal law-enforcement officers as they continue operations to remove the worst of the worst from Los Angeles,” said Department of Homeland Security spokeswoman Tricia McLaughlin.

At roughly 5 p.m. local time Tuesday, protesters in downtown Los Angeles were marching through the streets, chanting, “Whose streets? Our streets.” Stores were being boarded up as the march went by.

As the march reached the federal building, police were waiting with shields. The protesters moved on without a clash.

Hours earlier, police had surrounded a group of protesters outside a detention center. Demonstrators were lined up against the wall while they were arrested.

Juan Pantoja, 47, said his brother was caught up in the arrests while riding his scooter past the protest. “It’s good they’re protesting, but all this vandalism is out of hand,” Pantoja said. “Cops shooting people with rubber bullets is out of hand too.”

The unusual decision to deploy active-duty troops was the first time in more than three decades that Marines have been sent into a U.S. city to address civil unrest.

Local elected officials have said that Trump’s response has at times caused the protests to intensify. California officials on Tuesday urged a federal judge in San Francisco to intervene and block the National Guard or Marines from being used for law enforcement.

“Federal antagonization, through the presence of soldiers in the streets, has already caused real and irreparable damage to the City of Los Angeles, the people who live there, and the State of California. They must be stopped, immediately,” the state said in a court filing. A hearing has been set for Thursday.

Defense Secretary Pete Hegseth , in a hearing before the House Appropriations Committee, also defended the deployment on Tuesday, describing protesters as “rioters, looters and thugs” who endangered federal agents.

The mission will cost the Pentagon at least $134 million for additional troop pay, food, transportation and other logistics, according to Bryn MacDonnell , the Pentagon’s acting comptroller, who testified alongside Hegseth.

Trump said in Tuesday’s speech he decided to deploy thousands of National Guard troops and Marines to protect law enforcement from what he described as “attacks of a vicious and violent mob, and some of the radical left.” The protesters, he said, “are animals.”

Earlier on Tuesday, the president warned that any protesters who show up at the military parade to celebrate the Army’s anniversary in Washington, D.C., on Saturday “will be met with very heavy force” as well.

Los Angeles resident Alex Navas said police shot him with a rubber bullet during a protest on Monday. The 33-year-old said he was trying to help his wife, Jackie, who had been pushed by law enforcement, when he was shot.

Both Alex and Jackie Navas were charged, the couple said, but that didn’t stop them from joining a march through downtown Los Angeles on Tuesday.

“I’m protesting for our rights,” Alex Navas said.

Write to Jack Morphet at jack.morphet@wsj.com , Victoria Albert at victoria.albert@wsj.com and Nancy A. Youssef at nancy.youssef@wsj.com