(CNN) Three civilians were killed Sunday when a Phoenix firetruck crashed into a passenger vehicle, according to local authorities.

Phoenix police told CNN affiliate KTVK the firetruck was on its way to a structure fire nearby when it collided with a pickup truck around 9:15 a.m. local time.

Sgt. Vince Lewis told reporters the deceased were an adult male, an adult female and a child, approximately 6 months old, who had been in a child's seat in the rear of the vehicle.

The cause of the accident was being investigated Sunday afternoon, said Lewis. Investigators with the vehicular homicide unit had not determined a cause.

"It appears, preliminarily, at this time, that the pickup truck turned left in front of the firetruck," he said. "But again, I want to give our investigators the time to work through this."

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