Demonstrators torched cars and scuffled with  security forces in Los Angeles on Sunday as police kept protestors away from the National Guard troops President Donald Trump sent to the streets of the second biggest US city.

Unrest broke out for a third day, with protestors angry at action by immigration officials that have resulted in dozens of arrests of what authorities say are illegal migrants and gang members.

The raids -- which began in broad daylight in a city with a large Latino population -- were always likely to spark reaction among the public in the liberal city.

But opponents say Trump, who has made clamping down on illegal migration a key plank of his second term, was deliberately stoking tensions with his deployment of California's National Guard, a stand-by military usually controlled by the state's governor, Gavin Newsom.

"We didn’t have a problem until Trump got involved," Newsom wrote on X.

"This is a serious breach of state sovereignty — inflaming tensions while pulling resources from where they’re actually needed. Rescind the order. Return control to California," he added.

At least three self-driving Waymo cars were burning on Sunday afternoon, with two others vandalized as protestors roamed around a limited area in downtown Los Angeles.

Traffic was halted on a key freeway for over an hour while scores of people thronged the roadway. They were moved off by California Highway Patrol officers, who used flash-bangs and smoke grenades.

But after a limited early confrontation between federal agents from the Department of Homeland Security and a few dozen protestors at a detention center, the clashes all involved local law enforcement.

By early afternoon LAPD officers established containment lines some distance from federal buildings, preventing contact between angry demonstrators and the scores of armed National Guardsmen from the 79th Infantry Brigade Combat Team, who had gathered in helmets and camouflage gear.

'TROOPS EVERYWHERE'

Trump, asked about the use of troops, was unrepentant, hinting instead at a more widespread deployment in other parts of the country.

"You have violent people, and we are not going to let them get away with it," he told reporters. "I think you're going to see some very strong law and order."

Responding to a question about invoking the Insurrection Act -- which would allow the military to be used as a domestic police force -- Trump said: "We're looking at troops everywhere. We're not going to let this happen to our country."

US Northern Command, part of the Department of Defense responsible for national defense, said "approximately 500 Marines...are in a prepared to deploy status should they be necessary to augment and support" the ongoing federal operations.

The National Guard is frequently used in natural disasters, and occasionally in instances of civil unrest, but almost always with the consent of local authorities.

Trump's deployment of the force -- the first over the head of a state governor since 1965 -- was criticized by Democrats, including former vice president Kamala Harris who called it "a dangerous escalation meant to provoke chaos."

'INTIMIDATION'

But Republicans lined up behind Trump to dismiss the pushback.

"I have no concern about that at all," said House Speaker Mike Johnson, accusing Newsom of "an inability or unwillingness to do what is necessary"

Demonstrators told AFP the purpose of the troops did not appear to be to keep order.

"I think it's an intimidation tactic," Thomas Henning said.

"These protests have been peaceful. There's no one trying to do any sort of damage right now and yet you have the National Guard with loaded magazines and large guns standing around trying to intimidate Americans from exercising our first amendment rights."

Estrella Corral said demonstrators were angry that hard-working migrants who have done nothing wrong were being snatched by masked immigration agents.

"This is our community, and we want to feel safe," she told AFP.

"Trump deploying the National Guard is ridiculous. I think he's escalating, he's trying to make a show for his agenda."

Marshall Goldberg, 78, told AFP that deploying Guardsmen made him feel "so offended."

"We hate what they've done with the undocumented workers, but this is moving it to another level of taking away the right to protest and the right to just peaceably assemble," he said.

Raids by the Immigration and Customs Enforcement (ICE) agency in other US cities have triggered small-scale protests in recent months, but the Los Angeles unrest is the biggest and most sustained against Trump's immigration policies so far.

A CBS News poll taken before the Los Angeles protests showed a slight majority of Americans still approved of the immigration crackdown.