Pro and anti-Trump protesters clashed in California

Clashes erupted on Saturday in a Berkeley, California park where supporters and opponents of US President Donald Trump were holding competing rallies. At least 20 arrests were made as police struggled to keep the two camps apart.

As fist fights broke out between the two sides and people threw bottles and cans over a barricade separating them, police resorted to using to an explosive device at one point in a bid to restore order.

* April 15: A Trump supporter runs at protesters while being pepper sprayed at a "Patriots Day" free speech rally on April 15, 2017 in Berkeley, California. More than a dozen people were arrested after fistfights broke out at a park where supporters and opponents

Several people were observed with bloodied faces and minor injuries, but there was no official word on casualties from authorities. Media, citing police, reported that at least 11 people were injured.

Police said more arrests could follow after video shot during the melee was reviewed.

* April 15: Trump supporters clash with protesters at a "Patriots Day" free speech rally on April 15, 2017 in Berkeley, California. More than a dozen people were arrested after fistfights broke out at a park where supporters and opponents of President Trump had gathered.

The trouble unfolded when hundreds of Trump opponents staged a counter-rally alongside an event billed as a "Patriots Day" free-speech rally and picnic, organised by mostly Trump supporters.

Between 500 and 1,000 people were in the park as the rallies peaked, according to an estimate by a Reuters reporter.

Among the Trump opponents were some counter-protesters dressed in black and wearing masks. The other side included self-described "patriots" and "nationalists", Trump supporters, free speech advocates, and other groups.

* A pro-Trump supporter bleeds after being hit by a counter-protester during the Patriots Day Free Speech Rally in Berkeley in California, US. April 15, 2017.

Daryl Tempesta, 52, who said he served in the US Air Force near the end of the Cold War, went to the rally to show his support for Trump.

"As a veteran, I like the track America is on, and that Trump is willing to stand and say we are still America and we are not going to be globalist, we're not going to be a communist country," Tempesta said. "That's a message I can get behind."

* April 15: Trump supporters clash with protesters at a "Patriots Day" free speech rally on April 15, 2017 in Berkeley, California. More than a dozen people were arrested after fistfights broke out at a park where supporters and opponents of President Trump had gathered.

At least 100 people from both camps eventually moved out of the park and into one of the city's main intersections, where they continued to fist fight, hurl insults and chant at each other.

The police presence was light there, and only two or three officers were seen near the crossroads.

* April 15: Trump supporters clash with protesters at a "Patriots Day" free speech rally on April 15, 2017 in Berkeley, California. More than a dozen people were arrested after fistfights broke out at a park where supporters and opponents of President Trump had gathered.

Thousands protested at the University of California, Berkeley after alt-right Milo Yiannopolous was invited to speak on campus. Berkeley has a long history of liberal activism and the University of California, Berkeley, was a centre of protests in the 1960s.

* Conservative demonstrators and opposition against U.S. President Donald Trump fight during a Patriots Day Free Speech Rally in Berkeley, California, U.S., April 15, 2017.