CONCORD, N.H. --

A parked, unattended ambulance rolled down a hill and into the side of a home early Thursday morning.

No one was seriously injured in the crash, but police said if it had happened a half hour later, the area would have been packed with students on their way to high school and employees of a nearby hospital.

Police said the Care Plus ambulance was at the Presidential Oaks nursing home to pick up a patient. When the driver went inside the building, the vehicle started rolling.

The ambulance traveled across a lawn and down a hill, knocking down part of a wall and sending a tree into a car that was heading west on Pleasant Street.

"There was damage to the car," Sgt. Mike McGuire said. "Minor damage, maybe a little more than that. Nobody was injured or reported injuries at this time."

The ambulance then continued across Pleasant Street and came to rest against a house. Witness Keith Johnson rushed to help, only to find there wasn't anyone inside the vehicle.

"Completely empty," Johnson said. "The doors were closed, the engine was off. I thought maybe someone was in it. I opened the doors up, and no one was in there."

The driver of the ambulance has not been identified, and the company is expected to issue a statement later Thursday.

The nursing home is also conducting its own investigation, but administrator Anne Purington said she is confident the residents were not at risk.

"Our residents are supervised by us," she said. "There's always two people in attendance. We are very confident that the safety of our residents was not compromised in this situation."

Police said the investigation will take a couple of days. They said that so far, there is no indication of anything mechanically wrong with the ambulance.