Shrapnel from artillery rounds fired by the U.S. Marine Corps during a celebration in front of Vice President JD Vance and Secretary of War Pete Hegseth detonated prematurely and struck a patrol car, the California Highway Patrol said.

The artillery rounds were fired over Interstate 5 near Camp Pendleton in San Diego County as part of a military demonstration for the Marine Corps’ 250th anniversary.

The live fire demonstration also coincided with “No Kings” protests against President Donald Trump and his administration that were occurring around Southern California and across the country.

 A 17-mile stretch of the busy freeway that connects Los Angeles to San Diego was shut down during the event by the California Highway Patrol. The stretch of freeway is typically used by over 80,000 people every day, according to the agency.

California Gov. Gavin Newsom’s office said it was notified by the federal government Saturday morning that the military planned to shoot live artillery over the heavily traveled freeway, prompting highway patrol officers to temporarily close the freeway.

Last week, the military said that mortar rounds would not be fired over the freeway and said no freeways or roads would be impacted by the event. Military officials said all activities would be strictly confined to training fields at Camp Pendleton and would not impact public areas. 

But on Saturday morning, the federal government requested that the state change electronic highway signs to read “LIVE WEAPONS OVER FREEWAY,” according to the California Highway Patrol. 

Freeway signs all around Southern California warned drivers that live fire was in the vicinity of the freeway around Camp Pendleton.

ABC News has reached out to the Marine Corps, Camp Pendleton and the Trump administration for a comment.

For hours on Saturday, drivers in Southern California were stuck in gridlock on the freeway or had to take lengthy detours.

During that time, shrapnel allegedly rained down on the freeway in the closure zone, according to CHP.

In a police report obtained by ABC News, CHP says a patrol SUV was struck with shrapnel. That SUV had “an approximate two-inch by half-inch piece of shrapnel on the hood of the patrol vehicle,” according to the report.

The agency says in the report that the shrapnel made a dent in the hood.

Additionally, patrol officers stated an officer working the freeway closure heard “what sounded like ‘pebbles’ falling on his CHP BMW motorcycle.” 

CHP says it immediately alerted the Marine Corps that a mortar round did not clear Interstate 5 and that shrapnel was falling around the freeway.  At that point, the Marine Corps, according to the CHP, immediately cancelled firing additional live ordinance over the freeway.

A safety sweep was conducted on the freeway to look for more shrapnel, but none was found.

Camp Pendleton officials told Fox News Digital that an investigation has been initiated to determine the incident’s root cause. “The demonstration went through a rigorous safety evaluation, and deliberate layers of redundancy, to ensure the safety of fellow citizens,” the statement to Fox reads in part.

In response to the apparent premature detonation and the firing of ordnances over the freeway, Newsom wrote on X on Sunday, “We love our Marines and owe a debt of gratitude to Camp Pendleton, but next time, the Vice President and the White House shouldn’t be so reckless with people’s lives for their vanity projects.”

The California Highway Patrol said it is requesting an after-action review with the federal government to discuss public safety.