Los Angeles police said "mass arrests" were underway as people gathered on downtown streets after an overnight curfew went into effect following days of protests against immigration enforcement raids. California Governor Gavin Newson earlier took legal action against President Donald Trump's mobilisation of National Guard troops and Marines to quell the protests.

Los Angeles leaders retained a curfew through Wednesday morningas local officials sought to get a handle onproteststhatDonald Trumpclaimed were an invasion by a "foreign enemy."

Looting and vandalism has scarred the heart of America's second biggest city as largely peaceful protests overimmigrationarrests turned ugly after dark.

"I have declared a local emergency and issued a curfew for downtown Los Angeles to stop the vandalism, to stop the looting," Mayor Karen Bass told reporters late on Tuesday.

One square mile (2.5 square kilometers) of the city's more-than-500 square mile area were set to be off-limits between 8pm and 6am for everyone apart from residents, journalists and emergency services, she added.

Police later said they were carrying out "mass arrests" of protesters defying the overnight curfew.

"Multiple groups continue to congregate on 1st St between Spring and Alameda" within the designated downtown curfew area, the Los Angeles Police Department wrote on X. "Those groups are being addressed and mass arrests are being initiated. Curfew is in effect."

One protester told AFP the arrest of migrants in a city with large foreign-born and Latino populations was the root of the unrest.

"I think that obviously they're doing it for safety," she said of the curfew.

"But I don't think that part of the problem is the peaceful protests. It's whatever else is happening on the other side that is inciting violence."

Small-scale and largely peaceful protests marred by eye-catching acts of violence began Friday in Los Angeles as anger swelled over ramped up arrests by immigration authorities.

At their largest, a few thousand people have taken to the streets, but smaller mobs have used the cover of darkness to set fires, daub graffiti and smash windows.

Read moreLos Angeles immigration protests: Five key points to know

Overnight Monday 23 businesses were looted, police said, adding that more than 500 people had been arrested over recent days.

Protests have also sprung up in cities around the country, includingNew York, Atlanta, Chicago and San Francisco.

'Provide protection'

Trump has ordered 4,000 National Guard to Los Angeles, along with 700 active-duty Marines, in what he has claimed is a necessary escalation to take back control -- despite the insistence of local law enforcement that they could handle matters.

Amilitaryspokeswoman said the soldiers were expected to be on the streets later Tuesday or some time on Wednesday.

Their mission will be to guard federal facilities and to accompany "federal officers in immigration enforcement operations in order to provide protection."

ThePentagonsaid the deployment would costUStaxpayers $134 million.

Photographs issued by the Marine Corps showed men in combat fatigues using riot shields to practice crowd control techniques at the Naval Weapons Station Seal Beach.

'Behaving like a tyrant'

Two dozen miles (40 kilometers) north, the sprawling city of Los Angeles spent the day much as it usually does: tourists thronged Hollywood Boulevard, tens of thousands of children went to school and commuter traffic choked the streets.

But at a military base in North Carolina, Trump was painting a much darker picture.

"What you're witnessing inCaliforniais a full-blown assault on peace, on public order and national sovereignty, carried out by rioters bearing foreign flags with the aim of continuing a foreign invasion of our country," he told troops at Fort Bragg.

"This anarchy will not stand. We will not allow federal agents to be attacked, and we will not allow an American city to be invaded and conquered by a foreign enemy."

California GovernorGavin Newsom, aDemocratwho has clashed with the president before, said Trump's shock militarization of the city was the behavior of "a tyrant, not a president."

"Sending trained warfighters onto the streets is unprecedented and threatens the very core of our democracy," he said.

In a filing to the US District Court in Northern California, Newsom asked for an injunction preventing the use of troops as any kind of policing force, and demanding they be confined to guarding federal buildings.

Read moreGavin Newsom: California's governor takes on Trump, woos embattled Democrats

District Judge Charles Breyer scheduled a hearing on the motion -- which charges Trump and Defense Secretary Pete Hegseth have violated the US Constitution -- for Thursday.

'Incredibly rare'

Trump's use of the military is an "incredibly rare" move for a US president, Rachel VanLandingham, a professor at Southwestern Law School in Los Angeles and a former US Air Force lieutenant colonel, told AFP.

US law largely prevents the use of the military as a policing force -- absent the declaration of an insurrection, which Trump again mused about on Tuesday.

Trump "is trying to use emergency declarations to justify bringing in first the National Guard and then mobilizing Marines," said law professor Frank Bowman of the University of Missouri.

(FRANCE 24 with AFP and AP)

Originally published on France24