California on Saturday became the first state to ban most law enforcement, including federal immigration agents, from covering their faces while conducting official business under a bill signed by Democratic Governor Gavin Newsom.

The ban is California's direct response to a recent series of immigration raids in Los Angeles where federal agents wore masks while making mass arrests.

The raids prompted a dayslong protest across the city and led President Donald Trump to deploy National Guard troops and Marines to the area.

Newsom said California, where 27% of residents are foreign-born, celebrates diversity.

"It’s what makes California great. It’s what makes America great. It is under assault,” he said at a news conference in Los Angeles.

The governor signed the bill in Los Angeles, flanked by state lawmakers and immigrant community members.

He added he was "really proud" of the California and "our state of mind" in pushing back against "these authoritarian tendencies and actions of this administration”.

But it's unclear how — or whether — the state can enforce the ban on the federal agents who have been carrying out those raids.

The new law prohibits neck gaiters, ski masks and other facial coverings for local and federal officers, including immigration enforcement agents, while they conduct official business.

It makes exceptions for undercover agents, medical masks such as N95 respirators or tactical gear. It doesn't apply to state police.

Trump administration officials have consistently defended the practice.

They argue that immigration agents have faced strident and increasing harassment in public and online as they have gone about their enforcement in service of Trump’s drive toward mass deportation, and hiding their identities is for their and their families’ safety.

Federal agents are already instructed to identify themselves and wear vests with ICE or Homeland Security markers during operations, Homeland Security Assistant Secretary Tricia McLaughlin said in a statement this week.

Newsom on Saturday also signed legislation to prevent immigration agents from entering schools and health care facilities without a valid warrant or a judicial order and to require schools to notify parents and teachers when immigration agents are on campus.

Assembly member Al Muratsuchi, D-Torrance said that students could not learn "if they live in fear of being deported", adding the California Safe Haven Schools Act sent a clear message to the president: "Keep ICE out of our schools.’”