US riot police and protesters clashed in downtown Los Angeles following federal immigration raids across the city in which dozens of people were reportedly taken into custody.

A Homeland Security Investigation Spokesperson told the Los Angeles Times that federal agents were executing search warrants related to the harbouring of people illegally in the country.

Security forces lined up wielding batons and what appeared to be tear gas rifles after authorities ordered crowds to disperse around dusk. On Friday, aerial footage showed armed immigration officers using unmarked vans to detain multiple people as crowds gather.

An LA police spokesperson said police on the scene of the protest had declared an unlawful assembly, meaning that those who failed to leave the area were subject to arrest.