Four North Carolina firefighters were among five people injured following a collision between a fire apparatus and a tractor-trailer Friday.

Concord firefighters were responding to a call when the crashed occurred, WCNC-TV reports. It's not clear what led to the accident, but police are investigating the incident. 

Four firefighters were injured in the collision. They were taken to the hospital, and their injuries weren't considered life-threatening.

The tractor-trailer's driver also was taken to the hospital and is expected to recover.