A Fourth of July parade in eastern Iowa turned to mayhem on Sunday when a pair of runaway horses lunged into the crowd and trampled 24 people, many of them children. At least one person was killed, and several others were seriously injured.

The chaos took place when two horses pulling a buggy got spooked and charged into the crowd at the Heritage Day Parade, a decades-old tradition that attracts thousands to Bellevue, a town of 2,300 people nestled along the Mississippi River. Bellevue’s fire chief, Chris Roling, said the two horses, both at the rear of the parade, bumped into one another, knocking one horse’s bridle off and causing it to bolt, followed by the second horse.

“They took off down the street uncontrollably,” Chief Roling said in a telephone interview. “They went about six blocks  the horses and the carriages behind them, running over children and adults along the parade route.”

“I’ve been doing this 35 years and I’ve never seen anything like it,” he added.

A spokesman for the Bellevue Police department said Janet Steines, 60, of Springbrook, whose husband was driving the carriage, died Sunday evening at the University of Iowa Hospital in Iowa City after she was taken there with injuries from the accident.