Similar protests are being held in dozens more cities including Washington, D.C., Chicago, New York and Palm Beach, Florida.
Police arrested protesters on suspicion of assault with a deadly weapon and other felony offenses.
Demonstrators participate in a march and rally to demand President Donald Trump release his tax returns, Saturday, April 15, 2017, in NY.
It was not immediately clear what protesters were charged with, or whether there would be more arrests.
"I do not have any details but I was told they were transported to the hospital", Byron White with the Berkeley Police Department said.
Duelling pro- and anti-Trump rallies in the United States turned violent on Saturday as numerous fistfights broke out and protesters fired pepper spray into a crowd.
Trump backers and members of the so-called alt-right movement were holding a "free speech" rally at the park, while opponents of the movement, calling themselves anti-fascists, headed to the same spot at about 10 a.m.
In anticipation of the protests at Civic Centre Park in downtown Berkeley, California, the agency had banned items that could be used as weapons, such as pepper spray, mace, baseball bats and glass bottles.
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By the end of the event, the park was quickly crowded with tiger and bunny looking faces with chocolate stained lips. Children and parents frantically start running as the egg hunt begins.
Police donned gas masks as they used pepper spray on the crowd.
Trump, a billionaire property tycoon, released a financial statement but has kept his tax returns private, both during the election campaign and since taking office in January.
"Stand up, America! Stand up!" shouted a Trump supporter in the middle of Center Street with a bandage on his head and streaks of blood on a sign that read "Stop Liberal Intolerance". It was the third time the two sides were involved in violence since President Donald Trump took charge.
"The amount of people at the park for the demonstration was in the hundreds", he said. The other side included self-described "patriots" and "nationalists", Trump supporters, free speech advocates, and other groups.
We chose to show up anyway because this is our livelihood, said Tim Mueller, a farmer who owns the stall, surrounded by protesters on both sides.
The events were unrelated to 150 marches planned across the country on Saturday that called on Trump to release his tax returns.
However, in the city of Berkeley, Calif., things went left as Trump protesters and "March4Trump" supporters got into violent scuffles that left at least 21 arrested and 11 injured, according to CNN. It was a separate event from the many Tax Day protests that peacefully happened in several other cities across the country.
Organisers said marches took place in about 150 U.S. cities on Saturday.