Some 20 demonstrators were arrested on Thursday outside a Donald Trump campaign rally in southern California, where the Republican presidential front-runner vowed to his supporters to get tough on illegal immigration if elected.

Demonstrators smashed the window of a police squad car, marched in protest and blocked traffic as police in riot gear tried to disperse the crowd outside of the county fair grounds in Costa Mesa, California, according to local media and the Twitter account of the Orange County Sheriff's Department.

The department said on its Twitter account that about 20 arrests were made and that no major injuries were reported. Trump visited Costa Mesa, a city of more than 100,000 people, a third of whom are Hispanic or Latino, hoping to garner support in California where voters will go to the polls during the state's Republican primary on June 7.

During the campaign stop on Thursday, Trump promised to get tough on illegal immigration by building a wall on the border between Mexico and the United States, a popular theme of his presidential campaign, suggesting that a wall would stop drugs from coming into this country.

After the event, local news showed hundreds of demonstrators surrounding vehicles, waving Mexican flags and holding signs in protest of Trump outside of the Orange County Fair and Event Center. Trump has come under fire from rivals for fueling unrest with his rhetoric as several of his rallies around the country have been met by protests during the last several months.