Shrapnel from artillery that was detonated during celebrations for the US Marine Corps hit at least two vehicles on a California highway on Saturday, officials have said.

The event, celebrating the Marines’ 250th birthday, was attended by Vice President JD Vance, and included live munitions being fired. The California Highway Patrol said one “detonated overhead prematurely” and struck two vehicles that were part of Vance’s protective detail.

It came as state officials and the White House fought over a decision to close part of Interstate 5 for the event in southern California.

“Firing live rounds over a busy highway isn’t just wrong – it’s dangerous,” Governor Gavin Newsom, a Democrat, said.

The highway patrol said no injuries were reported and they notified the Marine Corps, which then cancelled firing any further munitions.

“This was an unusual and concerning situation,” Border Division Chief Tony Coronado said in a statement, adding that such exercises are not common over an active freeway.

Newsom said he closed a section of the Interstate 5 “due to extreme life safety risk and distraction to drivers, including sudden unexpected and loud explosions”.

But before they were aware of the mishap, officials in the vice-president’s office had disputed that the demonstration was dangerous, and accused the California governor of trying to stoke fears.

The BBC has contacted the White House and vice-president’s office about the shrapnel incident.

“If Gavin Newsom wants to oppose the training exercises that ensure our Armed Forces are the deadliest and most lethal fighting force in the world, then he can go right ahead,” William Martin, Vance’s communications director, told CNN, before reports about the incident were known.

“It would come as no surprise that he would stoop so low considering his pathetic track record of failure as governor.”

Newsom responded to the military mishap by saying that “Donald Trump and JD Vance put lives at risk to put on a show”. He added that if they wanted to honour troops, they should work to reopen the federal government, which ran out of funding at the beginning of October.

The First Marine Expeditionary Force at Camp Pendleton said in a statement that it was aware of the incident concerning a 155-millimeter shell fired during the event, and that an investigation was underway.

“The demonstration went through a rigorous safety evaluation, and deliberate layers of redundancy, to ensure the safety of fellow citizens,” the statement read.

“Following established safety protocols, firing was suspended. No injuries occurred and the demonstration concluded as scheduled.”

In a police report, California Highway officers said the two damaged vehicles, which had been used as part of Vance’s detail, were then sent to guard the freeway and keep it closed during the event.

The officers wrote in a report that they saw the artillery round fail to clear the highway and explode near southbound lanes.

One of the officers said it sounded like pebbles were raining down on his patrol motorcycle. Several pieces of shrapnel were found, including one that dented the hood of a patrol car.

The demonstration was the largest in a decade in the continental US, the Marines said, and involved fighter jets, Navy vessels, helicopters and live fire from a towed howitzer.

During his remarks in front of hundreds of marines, Vance recalled his time in the force, railed against the government shutdown and critiqued previous military diversity initiatives.

“I would not be here today, I would not be the vice president of the United States, I would not be the man I am today were it not for those four years that I served in the Marine Corps,” he said.

Vance spent four years in the Marines and served a tour in Iraq in 2005.

But his remarks largely focused on politics, and in part he attacked “woke” aspects of the military.

“It is our common purpose, it is our common mission and it is the fact that every single person here bleeds Marine Corps green,” he said.

One of the Trump administration’s focuses has been eliminating diversity initiatives, particularly within the Pentagon.

Vance also used the stage time to rail against the nearly three-week long government shutdown and put blame on Democrats, particularly Senate Minority Leader Chuck Schumer.

“I bring greetings today from our commander in chief, Donald J Trump, and he wanted me to tell each and every single one of you that he’s proud of you, that he loves you and that despite the Schumer shutdown, he is going to do everything he can to make sure you get paid exactly as you deserve,” he said.

While thousands of federal workers are working without pay, the Defence Department is paying troops.