A wood platform holding live fireworks tipped over, sending the pyrotechnics straight into a crowd at the annual 4th of July show in Simi Valley, Calif.
Between 8,000 and 10,000 revelers were settling into their seats in the L.A. suburb for a fireworks display that never quite made it into the sky.
Instead, a bright plume of red and white bursts spread across the ground, injuring 28 people and sending others fleeing for safety. Take a look:
Police were investigating what led to the explosion, but said early indications show a platform designed and built to hold the fireworks gave way.
"For unknown reasons the structure that holds these ordinances collapsed," Stephanie Shannon of the Simi Valley Police said of the Fourth of July accident.
Four people were listed in serious condition, but their injuries were not life-threatening. Another 16 were taken to area hospitals with minor to moderate injuries.
The remainder of those affected were treated at the park where an emergency crew, already on hand as a safety precaution, set up a triage area.
A video clip on KCAL-TV shows a pair of firework blasts at or near the ground.
Another clip posted on YouTube shot from a distance shows three ground-level bursts; fireworks continue for almost another minute before stopping.
"There was a big boom, everybody started running down the street, people were screaming," Justice Allen, 17, of Simi Valley told the Los Angeles Times.
"Everybody was just terrified. People hid in bushes."
Authorities estimate people were about 900 feet away from where the fireworks were being launched, but that wasn't far enough to prevent injury.
One police officer who ran into the crowd when the blasts occurred had shrapnel tear through his leather belt and his clothing, Shannon said.
He had minor injuries to his back, according to police.
Shannon said most people responded admirably and left in an orderly fashion. A bomb squad was at the park to deactivate the remainder of the fireworks.