Several demonstrators were waving Mexican flags
At least 20 people have been arrested after scuffles broke out between protesters and supporters of Donald Trump in California.
The violence erupted in the city of Costa Mesa, as the US presidential hopeful held a rally there on Thursday evening attended by thousands of backers.
The protests were mostly peaceful as the Republican front runner gave his speech but later they became more rowdy.
The front and back windows of a police car were smashed and its roof was dented.
One man jumped on the top of the vehicle and after he got off, a group of people tried to flip it over.
Others sprayed graffiti on the car as well as the marquee of the Pacific Amphitheatre where Mr Trump was holding his event.
Dozens of cars - including those of Trump supporters trying to leave - were stuck in the street as several hundred demonstrators blocked the road, some waving Mexican flags.
One man suffered a bloodied face in a scuffle as he tried to drive out of the arena.
Police in riot gear and on horseback pushed the crowd back and away from the venue.
Some protesters were objecting to the republican front runner's immigration proposals and the comments he has made about Mexicans during the campaign.
He has accused the southern neighbour of sending its "rapists" and criminals to the US and said if he becomes president, he plans to build a wall along the border with Mexico to keep them out.
No major injuries were reported following the violent scenes in Costa Mesa.
Meanwhile six people, including a police officer, were temporarily isolated and monitored after a suspicious white powder was found at Trump Tower in New York City.
A worker discovered the substance after they opened an envelope sent to the billionaire's campaign office there. Police were called and the powder was later found to be harmless.