Los Angeles Mayor Karen Bass has declared an overnight curfew in the downtown area of the United States’ second-largest city, after several nights of unrest and vandalism.

“I have declared a local emergency and issued a curfew for downtown Los Angeles to stop the vandalism, to stop the looting,” she told reporters.

The announcement comes as US President Donald Trump vowed to “liberate” Los Angeles from what he claimed was an invasion by a “foreign enemy” as California’s leaders went to court seeking to prevent the President sending thousands of troops on to the streets.

As a fifth day of protests unfolded in the second largest US city, several hundred people gathered at a building being used to detain those arrested in Trump’s signature immigration crackdowns.

US President Donald Trump gives a thumbs up as he speaks at Fort Bragg, a US Army military installation, near Fayetteville, North Carolina. Photo / Brendan Smoalowski, AFP

Officers from the Los Angeles Police Department (LAPD) moved in to make arrests as they pushed the crowd back from the building.

A short distance away around 100 people briefly made it on to a freeway, halting traffic.

Protests against immigration raids also emerged in New York on Tuesday, as several thousand people marched through the streets of Manhattan.

Small-scale and largely peaceful protests involving a few thousand people began Friday, with sporadic but isolated violence erupting as crowds dispersed and masked individuals confronted police.

Overnight Monday a mob in LA’s Little Tokyo area shot fireworks at officers in riot gear, who fired back with volleys of tear gas.

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Several businesses – including the Apple Store – were looted, and the LAPD said they had arrested 96 people.

Bass earlier said violence, crime and vandalism would not be tolerated, vowing police would hunt down wrongdoers.

But she stressed the majority of protesters have been peaceful – and that local law enforcement could easily cope.

“The unrest that has happened (is) a few blocks within the downtown area,” she said.

“It is not all of downtown, and it is not all of the city. Unfortunately, the visuals make it seem as though our entire city is in flames, and it is not the case.”

Bass slammed the deployment of 700 active-duty soldiers and 4000 National Guard troops, which the Pentagon said would cost taxpayers $134 million.

“What are the Marines going to do when they get here? That’s a good question. I have no idea,” she said.

The answer – at least on Tuesday – was training.

The Marine Corps issued photographs of men in combat fatigues using riot shields to practise crowd control techniques at the Naval Weapons Station Seal Beach.

‘Behaving like a tyrant’

Two dozen miles (40km) north, 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 of the city.

“What you’re witnessing in California is 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 Governor Gavin Newsom, a Democrat who has clashed with the President before, said Trump’s shock militarisation of the city was the behaviour 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.

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 mobilising Marines,” said law professor Frank Bowman of the University of Missouri.

- Agence France-Presse