Democratic US Senator Alex Padilla has been forcibly removed from a news conference held by Homeland Security Secretary Kristi Noem in Los Angeles.

Noem was offering the latest figures on immigration enforcement in the area, which has led to nearly a week of protests in the city, to members of the news media when Sen Padilla interrupted and started shouting a question.

Once removed from the room, the California senator was handcuffed.

Padilla's removal caused condemnation on both sides of the aisle, with fellow senators calling the arrest shocking and a "sickening disgrace" and the Trump administration dubbing it "disrespectful political theatre".

"I'm Senator Alex Padilla," he said as he was confronted by authorities. "I have questions for the secretary!"