An artillery shell detonated prematurely midflight Saturday during a Marines anniversary event attended by Vice President JD Vance, sending shrapnel flying toward California Highway Patrol vehicles, according to a report from the CHP.

The incident, which was first reported by The New York Times, occurred after California Gov. Gavin Newsom had warned about the danger of the event, which involved firing live artillery over Interstate 5, a busy highway in Southern California.

“The President is putting his ego over responsibility with this disregard for public safety,” Newsom said in a statement before the event. “Firing live rounds over a busy highway isn’t just wrong — it’s dangerous.”

The White House, meanwhile, had argued there were no “public safety concerns” associated with the exercises, citing guidance from leaders of the Marines.

Newsom and the White House had also sparred about the need to close down parts of Interstate 5, where the event was taking place. Newsom eventually shut down portions of the highway, despite claims from the White House that it was unnecessary.