Some type of gas was released Saturday morning into a crowd of protesters in Berkeley’s Martin Luther King Jr. Civic Center Park, a police spokesman said.
The protest between Trump and anti-Trump supporters is located near downtown Berkeley at 2151 Martin Luther King Jr. Way.
Spokesman Officer Byron White wasn’t sure when protesters started gathering but some were going to gather at 10 a.m. and others at noon.
Other groups may come later, he said.
Because of the release of the gas, police put on gas masks. At least four arrests have been made. White did not have any information on injuries.
Officers have encountered items at the protest that are prohibited such as flagpoles, a knife, a stun gun, helmets and signs and flags attached to poles.
Officers continue to monitor the protest and adjust their tactics, White said.