SAN FRANCISCO (KRON) – 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. The annual event attracts about 20,000 people.

There wasn’t a lot of room in between groups of people, so people couldn’t get up and run, according to Jane Imber.

While reports of fireworks malfunctioning at large display shows are rare, according to the U.S. Consumer Products Safety Commission, similar accidents have occurred in California in recent years.

A fireworks company blamed bad fireworks for a blast that injured more than three dozen people at a 2013 show in Simi Valley in Southern California and also triggered problems at more events in the area.

The cause of the Colorado malfunction is under investigation.