SIMI VALLEY, Calif. - An accidental explosion last night at a California fireworks show injured more than 30 people, four of them seriously, officials say.

The explosion happened at an annual Fourth of July fireworks display at a Simi Valley park, not far from Los Angeles. A platform holding the fireworks gave way, sending the pyrotechnics into the crowd as thousands of people looked on.

The victims ranged from 8 years old to 78, police say. A total of 20 people were taken by ambulance to area hospitals. Four suffered serious, but not life-threatening, injuries.

The show was staged by a Long Island-based company, Bay Fireworks. The company said in a statement that it regrets the injuries and plans a thorough investigation, with results to be made public.

Bay Fireworks has produced events for NASA, Walt Disney World, Legoland and the Republican National Convention, according to the company's website.

AP wire services contributed to this report.