U.S. immigration authorities extended activity in the Los Angeles area on Saturday in the wake of protests at a federal detention facility and a police response that included tear gas, flash-bangs and the arrest of a union leader.

Border Patrol personnel in riot gear and gas masks stood guard outside an industrial park in the city of Paramount, Calif., deploying tear gas as bystanders and protesters gathered on medians and across the street, some jeering at authorities while recording the events on smartphones.

"ICE out of Paramount. We see you for what you are," a woman announced through a megaphone, referring to U.S. Immigration and Customs Enforcement. "You are not welcome here."

One hand-held sign said, "No Human Being Is Illegal."

The boulevard was closed to traffic as U.S. Border Patrol circulated through the area. ICE representatives did not respond immediately to email inquiries about weekend enforcement activities."

Arrests by immigration authorities in Los Angeles come as U.S. President Donald Trump and his administration push to fulfil promises to carry out mass deportations across the country.

On Friday, ICE officers arrested more than 40 people as they executed search warrants at multiple locations, including outside a clothing warehouse, where a tense scene unfolded as a crowd tried to block agents from driving away.

Los Angeles Mayor Karen Bass said the activity was meant to "sow terror" in the nation's second-largest city.

In a statement on Saturday, ICE acting director Todd Lyons chided Bass for the city's response to protests.

"Mayor Bass took the side of chaos and lawlessness over law enforcement," Lyons said in a statement. "Make no mistake, ICE will continue to enforce our nation's immigration laws and arrest criminal illegal aliens."

Protesters gathered Friday evening outside a federal detention centre in Los Angeles, where lawyers said those arrested had been taken, chanting "set them free, let them stay!"

Other protesters held signs that said "ICE out of LA!" and led chants and shouted from megaphones. Some scrawled graffiti on the building facade.

Federal agents executed search warrants at three locations, including a warehouse in the fashion district of Los Angeles, after a judge found there was probable cause the employer was using fictitious documents for some of its workers, according to representatives for Homeland Security Investigations and the U.S. Attorney's Office.

Advocates for immigrant rights say people were detained on Friday by immigration authorities outside Home Depot stores and a doughnut shop.