AVON, Colorado -- Officials say nine people suffered minor burns during an accident at a fireworks show in Colorado.

Virginia Egger, the town manager in Avon, says a malfunction caused a fireworks shell to explode in its tube rather than firing into the sky Friday night. She says the misfired shell caused a rack of shells to tip, causing two or three shells to go off toward the crowd.

The accident occurred about 17 minutes into the 23-minute fireworks show over Nottingham Lake, bringing the event to a halt.

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"Police, fire and emergency medical staff responded to the incident in less than one minute," Deputy Fire Chief Greg Daly said in a statement. "Four ambulances were assigned to the event in addition to one paramedic supervisor, so experienced medical personnel were ready to respond quickly. The crowd was exceptional in its calm response to what could have been a much more serious incident."

The annual event attracts about 20,000 people as part of weekend Fourth of July holiday celebrations.

The cause of the malfunction is under investigation.