DURHAM — Fire destroyed a building in which two people had been sleeping shortly before midnight Thursday on Mill Pond Road, fire officials said.

A dog awakened the two people asleep in an outbuilding that measured 60 feet by 20 feet at 82 Mill Pond Road, Fire Chief Rob Tripp said Friday.

One of the occupants called 911 to report the fire after a dog woke them up. All three were able to get out of the building safely, but lost all of their possessions, Tripp said.

The fire appeared to have started outside of the building and made its way in, Tripp said.

Local firefighters cleared the building, then doused the flames. They were at the scene for roughly three hours, Tripp said.

“We believe it started on the outside deck and moved its way in,” Tripp said.

The cause of the fire was undetermined as of Friday morning and was still under investigation.

The fire was not considered suspicious, Tripp said.

He said fighting the blaze was made more difficult by the presence of multiple propane tanks “and ammunition that was firing off on arrival” of firefighters.

Firefighters from Freeport and Lisbon responded to the scene. Tanker trucks from Lisbon and Brunswick parked nearby. Pownal firefighters covered the Durham Fire Station.

The American Red Cross was alerted to help the occupants of the building.