Fighting broke out as people supporting or opposing U.S. President Donald Trump converged Saturday on Martin Luther King Jr. Civic Center Park in Berkeley, Northern California.

At least 13 people were arrested as police struggled to keeep the two camps separate. The City of Berkeley Police Department posted on its Twitter account images showing some "prohibited items," including a knife, removed from the site in the downtown park area.

Police initially said 15 people were arrested.

While witnesses put the number of Trump supporters and opponents at hundreds, authorities in the city north of San Francisco did not gave an estimate for the size of the crowd but did cite a "large number of fights" to advise people to stay away from the area.

Trump supporters, some of them members of the alt-right movement, were there for a "free speech" rally.

The Trump opponents, who identified themselves as anti-fascists, arrived at about 10 a.m. to voice their anger against the movement and the president.

Fireworks were thrown in the crowds; and sticks, flagpoles and other objects banned for the park were collected by police, who erected a plastic barricade between the two camps.

"A large number of fights have occurred and numerous fireworks have been thrown in the crowds. There have also been numerous reports of pepper spray being used in the crowd," the police department said in a statement.

By 2:00 p.m., the crowd spread out but traffic around the area was still blocked.

There were reported injuries among people in the crowd, but police did not confirm any of the report.

Berkeley and the University of California, Berkeley, have been sites of a series of violent and non-violent protests since November last year, when Trump was elected president of the United States.

Source: Xinhua