A fireworks mishap in a town northwest of Los Angeles has left at least 28 people injured after an "unintended" detonation shot fireworks into a crowd during the Fourth of July display.
The incident occurred Thursday night in Simi Valley, Calif., about 35 miles northwest of Los Angeles. Between 8,000 and 10,000 revelers were settling into their seats when a platform holding live fireworks tipped over, sending the pyrotechnics into the crowd.
Authorities estimated that people were about 900 feet from where the fireworks were being launched
"Everybody started screaming and everything that was supposed to happen didn't happen," eyewitness Joanne Herrera told ABC News. "It was pretty frightening. And a block of wood … came shooting down into the side of my leg."
Rancho Santa Susana Community Park was evacuated and the show was halted after the incident, which took place at about 9:30 p.m.
Of the 28 injured, four were considered seriously injured, according to Cmd. Stephanie Shannon of the Simi Valley Police Department.
During the incident, fireworks ordnance -- the actual firework container with the explosive material and fuse -- were fired into the crowd. The injuries were consistent with projectile-type wounds, with shrapnel projected into victims' bodies.
"We saw at least two or three fireworks go sideways, horizontally and explode," said J.T. Alpaugh, a KABC-TV reporter who was watching the display with family. "And then it seemed like the barrage of fireworks started exploding at the base of the park, right near the soccer field at ground level.
Now, obviously, fireworks are designed to go up 200 feet in the air and explode. And we realized immediately that something was terribly, terribly wrong."
After the incident, fireworks were still on the field. Authorities evacuated the field, and waited for the Ventura County Fire Department bomb squad to respond to deactivate the unexploded fireworks.
The fire department said the injured were transported to Simi Valley Hospital, Las Robles Regional Hospital and Holy Cross Hospital.
"We're still in the process of sorting out exactly what happened and treating the injured and evacuating them to area hospitals," John Parks, the watch commander at the Simi Valley police department, said late Thursday.
Many of the injured were wrapped up with gauze with what appear to be burn-like injuries, and were being brought into ambulances with IV bags.
Police said fireworks accidentally detonated during the display. Precautionary measures taken ahead of the fireworks display were key to a quick response after the incident, Parks said.
"We had about 40 police personnel on scene, as well as fire and ambulance people who were staged at the part of the fireworks production for crowd and traffic control and security. So the response was really rapid and the people that were injured were attended to very quickly," he said.
The Independence Day event was sponsored by the support of the Rancho Simi Recreation and Parks District.
ABC News' Alex Stone and Rebecca Lee contributed to this report.