The closure of a 17-mile (27-kilometer) stretch of Interstate 5, which links Los Angeles and San Diego, snarled traffic for hours and set off another spat between California's liberal governor and Republican Donald Trump's White House.

"The President is putting his ego over responsibility with this disregard for public safety," said Governor Gavin Newsom, a frequent Trump critic who is expected to make a White House run in 2028.

"Firing live rounds over a busy highway isn't just wrong -- it's dangerous."

Signs near the interstate warned on Saturday: "Live weapons over freeway."

The order to shut the freeway came after California Highway Patrol officials warned that live munitions flying overhead would distract drivers on the oceanfront stretch of Interstate 5 near Camp Pendleton.

In a statement, the Marine Corps insisted there was no risk to the public.

"Artillery pieces have historically been fired during routine training from land-based artillery firing points west of the I-5 into impact areas east of the interstate within existing safety protocols and without the need to close the route," it said in a statement.

"This is an established and safe practice."

The massive Marine exercise featured fighter jet flyovers, amphibious ships, explosions in a simulated village and Navy SEALS dropping into the Pacific Ocean from helicopters.

In his address, Vance said the Trump administration was focused on supporting Marines and removing "woke" priorities that he argued have weakened the US armed forces.

"When officials try to shift focus to mandating diversity quotas, or they try to inject partisan politics into the American armed forces, they impede the Marine Corps's ability to do its best work.

"And that's why the secretary of war and the president of the United States have stood so firmly against that crap," Vance, a Marine veteran, told the assembled troops.

The Marine display came the same day that millions took to the streets from coast to coast in the United States to protest the hardline policies of the Trump administration, which have included the dismantling of diversity and equity programs.

In June, Trump ordered National Guard troops to Los Angeles to support federal officials in carrying out sweeping immigration raids and to tamp down local protests.

The deployment, which also included hundreds of Marines, was criticized by Newsom and local officials, who argued that the relatively small demonstrations could have been easily handled by city and state law enforcement.