National Guard troops clashed with protesters in Los Angeles as a third day of demonstrations against immigration raids turned violent.
Protesters blocked off a major road and set self-driving cars on fire as law enforcement used tear gas, rubber bullets and flash bangs to control the crowd.
Police declared an unlawful assembly in downtown LA, a warning that the crowd faced arrest if they did not disperse.
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 parked on the closed southbound 101 freeway. Officers ran under an overpass to take cover.
It was the third and most intense day of demonstrations against Mr Trump's immigration crackdown in the region, as the arrival of around 300 Guard troops spurred anger and fear among many residents.
The Guard was deployed to protect federal buildings, including the detention centre where protests were concentrated.
Los Angeles Police Chief Jim McDonnell said officers were "overwhelmed" by the remaining protesters. He added they included regular agitators who appear at demonstrations to cause trouble.
Several dozen people were arrested throughout the weekend. One was detained on Sunday for throwing a Molotov cocktail at police, and another for ramming a motorcycle into a line of officers.
Mr Trump responded to Mr McDonnell on Truth Social, telling him to arrest protesters in face masks.
"Looking really bad in L.A. BRING IN THE TROOPS!!!" he wrote.
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.
The move has sparked a row as Trump’s order went against the wishes of the state of California.
Governor Gavin Newsom said he requested the Trump administration withdraw its order to deploy 2,000 National Guard troops in Los Angeles County, calling it unlawful.
Mr Newsom accused Trump of trying to manufacture a crisis and violating California's state sovereignty. “These are the acts of a dictator, not a President,” he wrote in a post on X.
The White House disputed Newsom's characterisation, saying in a statement that “everyone saw the chaos, violence and lawlessness”.
Earlier, about a dozen National Guard members, along with Department of Homeland Security personnel, pushed back a group of demonstrators that amassed outside a federal building in downtown Los Angeles, video showed.
Trump called the demonstrators “violent, insurrectionist mobs” and said he was directing his cabinet officers “to take all such action necessary” to stop the “riots”.
Speaking to reporters in New Jersey, he threatened violence against demonstrators who spit on police or National Guard troops, saying “they spit, we hit”. He did not cite any specific incidents.
“If we see danger to our country and to our citizens, it will be very, very strong in terms of law and order,” Trump said.
National Guard troops were also seen in Paramount, in southeast Los Angeles, near the Home Depot, the site of altercations between protesters and police on Saturday.
Law enforcement faced off with a few hundred protesters in Paramount and 100 in downtown Los Angeles on Saturday, with federal officers firing gas canisters in efforts to disperse crowds, according to Reuters witnesses.
Authorities in Los Angeles arrested about 30 people on Saturday, including three on suspicion of assaulting an officer. The Los Angeles County Sheriff's Office said three deputies sustained minor injuries.
The FBI offered a $50,000 reward for information on a suspect accused of throwing rocks at police vehicles in Paramount, injuring a federal officer.
Despite Trump's rhetoric about the demonstrations, he has not invoked the Insurrection Act, an 1807 law that empowers a president to deploy the US military to suppress events like civil disorder. Asked on Sunday whether he was considering invoking the law, he replied “it depends on whether or not there's an insurrection”.
