OAKLAND, Calif. (AP) — Police say a group of anti-Trump demonstrators who gathered for a rally Wednesday afternoon swelled to more than 7,000 later in the night and caused havoc throughout downtown Oakland.

Police arrested 30 people and issued 11 citations for assault on an officer, vandalism, unlawful assembly, failure to disperse, and possession of a firearm.

Three Oakland officers were injured during the protests, though details of how they were hurt were not released Thursday.

Police called in mutual aid from a dozen law enforcement agencies, and during the protests three police cars from Pleasanton were damaged. Fire crews put out at least 40 fires throughout the night, including one fire that threatened a business.

Just after 8 p.m., officials say the crowd assaulted officers, tossing rocks, bottles, fireworks, M-80s, and Molotov cocktails at police.