US President Donald Trump has deployed troops amid unrest during immigration raids in Los Angeles.

"Looking really bad in L.A. BRING IN THE TROOPS," Trump stated in a post on Truth Social on Monday. In another post, he ordered the immediate arrest of anyone wearing a mask.

Trump stated the police chief reported increasingly aggressive protesters and a need to reassess the situation, urging immediate action.

Tensions in Los Angeles escalated on Sunday night as thousands of protesters took to the streets in response to Trump's deployment of the National Guard, blocking off a major freeway and setting self-driving cars on fire as law enforcement used tear gas, rubber bullets and flash bangs to control the crowd.

Roughly 300 National Guard members arrived in the city over the weekend, and Trump said he had authorised 2,000 members to deploy if needed. This appears to be the first time in decades that a state’s National Guard was activated without a request from its governor.

Gavin Newsom, a Democrat, told MSNBC that he planned to file suit on Monday against the Trump administration to roll back the Guard deployment, which he called "an illegal act, an immoral act, an unconstitutional act."

Trump has cited a legal provision that allows him to mobilise federal troops when there is "a rebellion or danger of a rebellion against the authority of the Government of the United States."

Starting Sunday morning, the troops stood shoulder to shoulder, carrying long guns and riot shields as protesters shouted "shame" and "go home." After some closely approached the guard members, another set of uniformed officers advanced on the group, shooting smoke-filled canisters into the street.

Minutes later, the Los Angeles Police Department fired rounds of crowd-control munitions to disperse the protesters, who they said were assembled unlawfully. Much of the group then moved to block traffic on the 101 freeway until state patrol officers cleared them from the roadway by late afternoon.

Nearby, at least four self-driving Waymo cars were set on fire, sending large plumes of black smoke into the sky and exploding intermittently as the electric vehicles burned.

By Sunday evening, police had issued an unlawful assembly order shutting down several blocks of downtown Los Angeles.

Flash bangs echoed out every few seconds into the evening.

Many protesters dispersed as evening fell and police declared an unlawful assembly, a precursor to officers moving in and making arrests of people who don't leave.

Some of those remaining threw objects at police from behind a makeshift barrier that spanned the width of a street and others hurled chunks of concrete, rocks, electric scooters and fireworks at California Highway Patrol officers and their vehicles.

Officers ran under an overpass to take cover.

The unrest in Los Angeles has become a flashpoint in Trump's signature effort to clamp down on irregular immigration.

The Republican president has pledged to deport record numbers of people who are in the country irregularly and to lock down the US-Mexico border, setting the ICE border enforcement agency a daily goal of arresting at least 3,000 migrants.

City Police Chief Jim McDonnell told a media briefing on Sunday evening that people had a right to protest peacefully but the violence he had seen by some was "disgusting" and the protests were getting out of control.

Police said they had arrested 10 people on Sunday and 29 the previous night, adding arrests were continuing.

Defense Secretary Pete Hegseth has said that the Pentagon is prepared to mobilise active-duty troops "if violence continues" in Los Angeles, saying Marines at nearby Camp Pendleton were on high alert.

Los Angeles Mayor Karen Bass blamed the Trump administration for inciting tension by sending in the National Guard.

She also condemned protesters who became violent. "I don't want people to fall into the chaos that I believe is being created by the administration completely unnecessarily," she told a press conference.

Vanessa Cardenas, head of the immigration advocacy group America's Voice, has accused the Trump administration of "trumping up an excuse to abuse power, and deliberately stoke and force confrontations around immigration."

About 60 people were arrested in San Francisco, police said late on Sunday.

San Francisco police "declared an unlawful assembly," they said on social media platform X. "Approximately 60 people were arrested, including juveniles."

Demonstrators said the purpose of the troops did not appear to be to keep order, with one calling it an "intimidation tactic."

"You have the National Guard with loaded magazines and large guns standing around trying to intimidate Americans from exercising our First Amendment rights," a protester Thomas Henning told the AFP news agency.

The protests did not reach the size of past demonstrations that brought the National Guard to Los Angeles, including the Watts and Rodney King riots, and the 2020 protests against police violence, in which Newsom requested the assistance of federal troops.

The last time the National Guard was activated without a governor's permission was in 1965, when President Lyndon B. Johnson sent troops to protect a civil rights march in Alabama, according to the Brennan Center for Justice.