WASHINGTON (AFP) - A malfunction at a fireworks display in California to celebrate American independence day sent exploding shells showering into a crowd of several thousand, injuring 28 people, police said.

Those injured in the mishap in Simi Valley near Los Angeles ranged in age from eight to 78, and four were left in serious condition, Simi Valley police spokesman Blair Summey told AFP.

The July 4 fireworks show at a park before a crowd of 8,000 to 10,000 people had just started when there was what Mr Summey called an ignition malfunction.

"Some of the shells went into the crowd," he said.

TV footage showed a bright, colourful explosion sending sparks showering down on people watching the show.

Simi Valley is about 25 miles (40 kilometers) west of Los Angeles.