WALNUT CREEK, Calif. (KRON) — Two people died Monday morning in a townhome fire in Walnut Creek, according to a tweet from the Contra Costa County Fire Department. The two-alarm fire broke out at Countrywood Townhomes.

Firefighters responded to the blaze at about 6:30 a.m. in a two-story townhome located at 1721 Countrywood Ct. near Treat Boulevard and Bancroft Road. When crews arrived, one of the three people living in the unit told firefighters that two other residents were still trapped inside on the second floor.

The residents died in the fire, according to Contra Costa County Fire Protection District Assistant Chief Chris Bachman. The residents who died in the fire were described as an elderly woman and her adult son. A small dog was also killed.

As of about 7:40 a.m. the fire was extinguished, according to fire officials on social media. Later, Contra Costa County Fire Department announced that the fire had been ruled accidental. The department says the fire is believed to have started in the first floor in a bed with a preliminary ignition source being smoking materials.

The fire department says that an oxygen machine nearby contributed to the rapid spread of the fire. The people who died in the fire reportedly died on the second floor, where the department says the dog’s body was also recovered.

The names of the two individuals who died in the fire were not released. The third victim who managed to escape and was treated at the scene, according to Contra Costa County Fire. The fire was contained to three units and is currently under investigation. There was damage to the townhomes on either side of the condominium. No other injuries were reported.

The fire department said the fire was accidental but was likely the result of a smoking materials in a first floor bedroom and that a nearby oxygen machine contributed to the rapid spread of the fire.

Bay City News contributed to this report.