A 15-year-old girl has been bitten by a police dog during a gun safety presentation at Nogales High School in Arizona on Thursday.

The dog’s handler and two other officers were putting on the gun safety presentation when the dog got out, police Capt. Heriberto Zuniga told the Nogales International.

Students suddenly ran into the classroom to tell them the dog was on the loose.

The dog’s handler ran out and secured his German shepherd, the Associated Press reports.

The 15-year-old girl student who was injured was taken to hospital with bites and scratches but wasn’t seriously hurt.

Heriberto Zuniga believes “somebody opened the door allowing the dog out of the vehicle”, a 2011 Ford Expedition specially outfitted as a canine unit.

The SUV was parked about 15 feet away from the classroom. The Santa Cruz County Sheriff’s Office is investigating.

The doors on the SUV are normally locked and officers were perplexed how a door could be opened from outside the vehicle, Heriberto Zuniga said.

The Ford Expedition was sent to a company in Tucson for inspection, and technicians discovered a fuse in the spring-loaded electronically controlled door had failed. It was replaced.

“Our first concern is the girl,” Heriberto Zuniga said.

The girl had bites to the arms and scratches on the lower back, but both Heriberto Zuniga and Principal Judith Mendoza-Jimenez said the teen was “OK”.

“We were extremely lucky. The dog is trained to bite and pull,” Heriberto Zunigo said.

“That didn’t happen. It appears in this case the dog realized the girl did not pose a threat.”

Judith Mendoza-Jimenez said: “It was an isolated incident. The dog got out of the car. We don’t know how.

“The girl saw the dog coming and she started running so the dog attacked her. Once she was on the ground the dog let her go.”

So far, nobody is confessing to having opened the door, “but we’re hoping that through interviews, the sheriff’s investigators will get some leads,” Heriberto Zuniga said.