At least one person was critically injured after a shooting at a demonstration in the western US city of Salt Lake City, police said, with local media reporting the shooting happened at a rally against US President Donald Trump.

Salt Lake City police department posted on social media that a person is in custody after the shooting.

Anti-Trump protests are taking place in at least 50 cities across the US.

In Los Angeles, thousands of people peacefully celebrated their defiance of US President Donald Trump on Saturday (local time) with music, marching, bubbles and balloons.

Then police unexpectedly moved in – and chaos and confusion broke out.

The demonstration, part of the nationwide “No Kings” day of protests across the nation, was by far the largest in more than a week of protests ignited by anger against immigration raids the Trump administration has been carrying out across the country’s second-largest city.

Like those before it, the protest had been largely peaceful. A march that began in the morning had finished, with demonstrators milling about on a sunny afternoon as the scene took on the air of a street festival.

Then police unexpectedly began moving people away from the area, igniting confusion and anger among demonstrators caught off guard and unsure of where to go.

Police on horseback pushed crowds back as law enforcement fired tear gas and flash-bang grenades hours ahead of an 8pm (local time) curfew.

A demonstrator throws a tear gas canister back at law enforcement during clashes that erupted after authorities declared an unlawful assembly during the "No Kings" protest against the Trump administration in Los Angeles. Photo / AFP

A police spokeswoman later told local TV channel KTLA that a “small group of agitators” had begun throwing rocks, bottles and fireworks at officers, prompting the decision to order the crowd to disperse.

If people refused to leave, “we will make arrests”, adding: “We have been patient all day.”

The clashes came after more than a week of demonstrations in Los Angeles against the immigration raids, which have rocked the city.

The protests have mostly been calm and contained to a small segment of downtown.

Police on horseback fire tear gas and rubber bullets to drive protesters back from the Edward R. Roybal Federal Building during the "No Kings" protests in Los Angeles. Photo / Getty Images

But at times they have spiralled into violence, which Trump pounced on to send in 4000 National Guard and 700 Marines – an exceedingly rare deployment of soldiers on US soil and against the will of local officials, who have repeatedly said the situation was under control.

The troops did not immediately appear to be involved in the clashes, with Los Angeles police and the sheriff’s department taking the lead.

‘No faux-king Trump’

Protest organisers expected rallies in all 50 US states, calling them the largest since Trump returned to office in January, with the aim of “rejecting authoritarianism, billionaire-first politics and the militarisation of our democracy”.

The day had begun with indigenous dancing at City Hall, as musicians played a light-hearted drumbeat on metal security barriers and street vendors filled the air with the smell of frying onions.

Then, beneath a giant balloon depicting Trump as a baby wearing a diaper, the demonstrators marched through downtown Los Angeles.

A 6m-tall balloon of US President Donald Trump in a diaper is seen among people taking part in a "No Kings" protest in Los Angeles, California. Photo / AFP

Parents brought their children, pet owners their dogs, and the lunchtime crowd at one popular market along the route enjoyed tacos and doughnuts as demonstrators passed by chanting while passing cars honked their support.

“No faux-king Trump,” read one sign as marchers chanted “Impeach Trump!”

Passing several armed National Guard in front of one federal building along the route, the protesters cried “Shame!”

Many of the signs had a light touch – “America, you in danger girl” read one, while another riffed on the acronym for Immigration and Customs Enforcement (Ice) and a favorite drink in Los Angeles: “Ice belongs in my matcha, not the streets.”

Protesters carry a banner representing the Preamble to the US Constitution in downtown Los Angeles during an anti-Trump "No Kings Day" demonstration in Los Angeles. Photo / Getty Images

Others were more pointed.

Many involved the words “Trump” and various expletives. Some showed images of the President as North Korean leader Kim Jong Un.

“Santa Monica Fascist”, read one sign with a photo of Trump’s top immigration adviser Stephen Miller, who is from the coastal city west of downtown Los Angeles.

People waved flags – predominantly US flags, some upside down as a signal of distress; but also the flags of Mexico, El Salvador, South Korea, the Palestinians, California’s state flag and the Pride flag celebrating LGBTQ rights.

Police fire tear gas to disperse demonstrators in front of the Federal Building during a march against US President Donald Trump in Los Angeles. Photo / Getty Images

“This isn’t a war zone,” protester Jennifer Franks, who was carrying her infant son, told AFP in front of City Hall earlier in the day.

“There is no reason to have the military called in here ... I want my child to grow up in a nation where common sense pervades.”

Wielding signs with messages like “No KKKings!”, “No crown for the clown” and “The Trump fascist regime must go now!”, the protests stood in stark contrast to the massive military parade in Washington later.

That parade was meant to commemorate the founding of the US Army, but also falls on the President’s 79th birthday.

In New York alone, tens of thousands of people, wearing raincoats and carrying colourful umbrellas, marched down Fifth Avenue in the downpour to the sound of drums, bells and crowd chants of “Hey, hey, oh, oh, Donald Trump has got to go!”

Actors Susan Sarandon and Mark Ruffalo were seen getting drenched among the protesters.

“It is essential for us to demonstrate that democracy is still strong in this country,” said Vikas Mehta, a 45-year-old doctor who was taking part in the demonstration with his wife and two children.

“We also want to show our children that ... when democracy was threatened ... we chose to participate,” he told AFP.

‘Outraged’

Nearby, a man carried a photo montage showing Marilyn Monroe delivering her famous rendition of “Happy Birthday Mr President”. But instead of a kiss, she was making an obscene gesture.

A few blocks away, Polly Shulman was preparing to join the march with her “Protect the Constitution” sign.

“I’m here because I’m miserable and outraged about how this administration is destroying the ideals of the American Constitution and committing many illegal and immoral acts,” the 62-year-old museum employee told AFP.

The most shocking thing, she said, was “the illegal deportations of law-abiding residents who did nothing wrong and who have the right to due process”.

A protester holds a placard during a march down the Benjamin Franklin Parkway to the Philadelphia Museum of Art during a nationwide "No Kings" rally in Philadelphia, Pennsylvania. Photo / AFP

They are “being kidnapped and disappeared and sent to torture prisons in foreign countries”, she lamented.

In March, the Trump administration expelled more than 250 Venezuelans to a mega-prison in El Salvador after accusing them of being members of the Tren de Aragua criminal gang, which it has declared a terrorist organisation.

At least four protesters were arrested at a separate, smaller protest against Trump’s immigration crackdown at New York’s Federal Plaza on Saturday (local time), police said.

‘Mad as hell’

“I think people are mad as hell,” Lindsay Ross, a 28-year-old musician, told AFP, urging the masses to show “the administration that we’re not going to take this”.

Bill Kennedy, a retired psychologist from Pennsylvania, was in Washington protesting a few hours before Trump’s big parade there.

“I’m tired of the current administration. I think they’re a bunch of fascists,” he said, describing the Trump parade as “ridiculous”.

Suzanne Brown in Boston also lamented the money spent on the parade “for one man’s vanity”.

Police on horseback fire tear gas and rubber bullets to drive protesters back from the Edward R. Roybal Federal Building during the protests in Los Angeles. Photo / Getty Images

Massive “No Kings” protests were also under way in Los Angeles, which in recent days has been rocked by demonstrations over the Trump administration’s immigration crackdown, as federal agents carried out brutal arrests of even law-abiding people without papers.

On Saturday (local time), protesters gathered in front of federal buildings shouting “You are not welcome here” at some of the 4000 National Guard members and 700 US Marines that Trump dispatched to the city against the wishes of city and state authorities.

With a giant orange Trump-in-a-diaper balloon towering above them, thousands filled the city streets, sporting slogans like “No faux-king way” and “Impeach Trump”.

Members of Russian feminist protest and performance art group Pussy Riot held up a large red banner in front of LA city hall warning: “It’s beginning to look a lot like Russia.”

Iris Rodriguez, 44, explained that her family arrived in the United States without papers.

“I find it really, really personal ... If this was my mom, if this were the 80s, this would be happening to her,” she told AFP.

“I was a little scared, but I refuse to be too scared to not come.”

The country-wide demonstrations overwhelmingly took place peacefully and without incident.

But in Culpeper, Virginia, police said a man had “intentionally” rammed his car into a group of protesters as they left the event.

The man, identified as 21-year-old Joseph R. Checklick jnr, “intentionally accelerated his vehicle into the dispersing crowd, striking at least one person with his vehicle”, police said, adding that he had been arrested and no injuries had so far been reported.

– Agence France-Presse