A melee erupted in a park in Berkeley, California, between supporters and opponents of US President Donald Trump holding competing rallies, resulting in at least 20 arrests as police struggled to separate the two camps.

Hundreds of protesters staged a counter-rally last Saturday in response to an event billed as a "Patriots Day" free-speech rally and picnic, organised by mostly Trump supporters.

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

Between 500 and 1,000 people were in the park as the rallies peaked.

REUTERS