At least 28 people were injured Thursday night when a fireworks display in Simi Valley, Calif., malfunctioned and fired into a crowd of 10,000.
"There was a big boom, everybody started running down the street, people were screaming," Justice Allen, 17, told the Los Angeles Times. "Everybody was just terrified. People hid in bushes."
The annual Fourth of July display held in a park 40 miles northwest of Los Angeles has been held for 43 years.
Four people were listed in serious condition, while 16 more were treated for minor to moderate injuries at nearby hospitals, the Associated Press reported.
The cause of the explosion is still under investigations.
Authorities believe the crowd was about 900 feet away from the platform where the fireworks were launched.
"For some unknown reasons the structure that holds these ordinances collapsed and caused them to be firing into the crowd," said Simi Valley police Cmdr. Stephanie Shannon.
A police officer, who ran into the crowd when the explosion occurred, had holes in his leather belt and clothing from shrapnel. Shannon said the officer injured his back.
Shannon said the fireworks then fired all in the same direction, at the crowd.
"They are going to travel the same distance across the park as they would in the air," she said. "The ones that had actually ignited that had to run their fuse were going directly into the crowd."
There was a triage area already set up in the park as a safety precaution.
In the following video, uploaded to YouTube by Supersportsj, revelers can be heard screaming and shouting for others to run. Viewer discretion is advised.