On Friday, U.S. Republican presidential candidate Donald Trump denounced protesters in California as thugs after another demonstration outside a political rally of his turned violent in the days before the state's presidential primary.

Videos posted on Twitter and online by local and national media showed clashes on Thursday evening in the street outside of the San Jose Convention Centre, where demonstrators fought and threw punches.

Hundreds of protesters waved Mexican flags, chanted anti-Trump slogans and burned Trump hats and at least one United States (US) flag.

Protesters, many angry over Trump’s rhetoric against illegal immigration, have gathered at Trump rallies for months. Trump, now the presumptive Republican presidential nominee for the 8 November election, cancelled a rally in Chicago in March after clashes broke out between his supporters and protesters.

San Jose Police Department reported 300 to 400 protesters had gathered outside the Trump rally on Thursday, where police formed lines to protect attendants exiting the rally.

One sergeant suffered minor injuries after a protester struck him with a metal object. Police reported four arrests.

Over 250 officers staffed the "all-hands on deck event," said San Jose Police Chief Eddie Garcia.

Trump has accused Mexico of sending drug dealers and rapists across the US border and has promised to build a wall and make Mexico pay for it.

“We are going to build that wall, don’t even think about it,” he said gave two thumbs up as his supporters chanted “build that wall.”