Hundreds of demonstrators have blocked traffic outside a venue in California where Republican presidential hopeful Donald Trump was holding a rally.
A police car had its windows smashed as Mr Trump spoke inside a hall in the Orange County Fairgrounds in Costa Mesa. Some 20 arrests were made.
Mr Trump has vowed to deport millions of illegal immigrants if he is elected US president in November.
He faces strong opposition in parts of California, particularly among Latinos.
California, the biggest prize for Republican candidates in the nomination race, holds its primaries on 7 June.
On Tuesday, Mr Trump called himself the Republican "presumptive nominee" after five new primary wins in the states of Connecticut, Delaware, Rhode Island, Maryland and Pennsylvania.
The Pacific Amphitheatre in Costa Mesa was filled to its capacity of about 18,000 people and hundreds more were turned away.
Heated exchanges could be heard between Trump supporters and the protesters outside, with supporters chanting "Build that wall! Build that wall!", a reference to the candidate's call for a barrier between the US and Mexico to stop illegal border crossings.
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