A faulty 4th of July fireworks display left 28 people injured during US Independence Day celebrations in Los Angeles.
The display was cancelled at Simi Valley Park after fireworks went off too close to the crowd.
At least four people were seriously injured though their injuries were not life-threatening, said emergency services.
Police believe that a platform built to hold the fireworks collapsed.
Simi Valley police commander Stephanie Shannon said: "For some unknown reasons the structure that holds these ordinances collapsed and caused them to be fired into the crowd."
Twenty of the victims were taken to local hospitals. The rest were treated at the scene by paramedics.
A bomb squad had to be used to render the remainder of the fireworks harmless.
Shannon said: "They are going to travel the same distance across the park as they would in the air. The ones that had actually ignited were going directly into the crowd."
Witness Tim Clunen said: "About 30 seconds into the show we saw that fireworks that were supposed to be shooting up high exploded on the ground.
"It appeared the fireworks were shooting off horizontally into the crowd and into the neighbourhood."
Justice Allen, 17, added: "Everybody was terrified. People hid in bushes."
The Independence Day celebrations at Simi Valley park attracts thousands of visitors every year.