PROVO, Utah — During the Fourth of July Independence Day celebrations, malfunctioning fireworks flew into the stands of a crowded Utah football stadium, striking spectators and sending up to six people to the hospital, according to authorities and the event organizer.

The accident occurred during the opening ceremony of the Stadium of Fire show, the main event of Provo's annual Freedom Festival at Brigham Young University's LaVell Edwards Stadium.

Organizers stopped the show for about 15 minutes while injured spectators received medical attention, said Emory Cook, spokesman for the Freedom Festival.

Six people were taken to hospital, Cook said, but the number of people hit by the fireworks and the severity of their injuries were not immediately known.

The cause of the accident – ​​fireworks were set off in the stadium as several jets flew over the stadium walls – is currently being investigated by local authorities.

Videos posted on social media show individual fireworks straying from the group, being sent into the sky above the field and landing in the rows of spectators in the stands of the outdoor arena. About 45,000 people attended the sold-out show, Cook said.

“Clearly there was a fireworks malfunction, but we are still trying to figure out how that happened,” Cook said.

Firefighters and paramedics were on the scene when the show began and were able to reach the injured audience members within a minute, said Jeanie Atherton, spokeswoman for Provo Fire and Rescue.

She said her department had taken only one person to the hospital, but other victims may have traveled in private vehicles.

The fireworks that didn't work inside the stadium were relatively small compared to the large pyrotechnics used in the show's finale, Cook said. Those larger fireworks are stored outside the stadium, he said.

After the accident, the BYU Police Department allowed organizers to continue the event, which featured the Jonas Brothers, KUTV reported.