Defense Secretary Pete Hegseth warned on Saturday the Pentagon was prepared to mobilise active-duty troops "if violence continues" in Los Angeles, saying the Marines at nearby Camp Pendleton were "on high alert".
Federal security agents on Saturday confronted protesters in the Paramount area in southeast Los Angeles, where some demonstrators displayed Mexican flags.
A second protest in downtown Los Angeles on Saturday night attracted some 60 people, who chanted slogans including "ICE out of L.A.!"
Trump signed a presidential memorandum to deploy the National Guard troops to "address the lawlessness that has been allowed to fester"the White House said in a statement.
Trump's border czar, Tom Homan, told Fox News the National Guard would be deployed in Los Angeles on Saturday.
California Governor Gavin Newsom called the decision "purposefully inflammatory".
He posted on X that Trump was deploying the National Guard "not because there is a shortage of law enforcement, but because they want a spectacle", adding: "Don't give them one. Never use violence. Speak out peacefully."
Trump posted on his Truth Social platform that if Newsom and Los Angeles Mayor Karen Bass can't do their jobs "then the Federal Government will step in and solve the problem, RIOTS & LOOTERS, the way it should be solved!!!"
The protests pit Democratic-run Los Angeles, where a significant portion of the population is Hispanic and foreign-born, against Trump's Republican White House, which has made cracking down on immigration a hallmark of his second term.
Senior White House aide Stephen Miller, an immigration hardliner, described the protests as a "violent insurrection."
The 1807 law empowers a president to deploy the US military to enforce the law and suppress events such as civil disorder.
The last time it was invoked was during the 1992 Los Angeles riots at the request of the California governor.
Video footage of the Paramount protest showed dozens of green-uniformed security personnel with gas masks lined up on a road strewn with overturned shopping carts as small canisters exploded into gas clouds.
Authorities began detaining some protesters, according to Reuters witnesses. There was no official information on any arrests.
"Now they know that they cannot go to anywhere in this country where our people are, and try to kidnap our workers, our people - they cannot do that without an organised and fierce resistance," said protester Ron Gochez, 44.
A first round of protests kicked off on Friday night after Immigration and Customs Enforcement agents conducted enforcement operations in the city and arrested at least 44 people on alleged immigration violations.
The Department of Homeland Security said in a statement that there were about "1,000 rioters" at the protests on Friday.
Reuters could not verify DHS's account.
Angelica Salas, executive director of immigrants' rights organisation Chirla, said lawyers had not had access to those detained on Friday, which she called "very worrying".
Trump has pledged to deport record numbers of people in the country illegally and lock down the US-Mexico border, with the White House setting a goal for ICE to arrest at least 3000 migrants per day.
But the sweeping immigration crackdown has also caught up people legally residing in the country, including some with permanent residence, and has led to legal challenges.
ICE, the Department of Homeland Security, and the Los Angeles Police Department did not respond to requests for comment on the protests or whether there had been any immigration raids on Saturday.
