Update: Smoking near oxygen machine likely sparked deadly Walnut Creek townhouse fire

WALNUT CREEK -- Firefighters said smoking materials and an oxygen machine were likely what sparked a deadly Walnut Creek townhouse fire that killed an elderly woman, her adult son and their small dog.

Firefighters responded about 6:30 a.m. to the fire in a two-story townhome at 1721 Countrywood Court, near Treat Boulevard and Bancroft Road.

Arriving crews found at least one of the units heavily involved in flames. They were told by one of the three people living in the unit that the other two residents were still inside on the second floor.

Less than two hours later, the fire was under control, but not before it claim the lives of two of the residents. A third victim escaped and was treated at scene.

The identities of the two victims were being withheld pending notification of next of kin. Authorities later confirmed the victims were an elderly woman and her adult son. Officials also said a small dog died in the fire. 

The oxygen machine helped it spread rapidly after the smoking materials ignited the fire in a first-floor bedroom, authorities said.

The victims were on the second floor and couldn't make it out. 

Contra Costa County Fire Protection District Assistant Chief Chris Bachman said the residents died inside the home.

The fire was contained to three units and its cause remains under investigation. There was damage to townhomes on either side of the condominium, but no other injuries were reported.

Authorities believe the fire started on the first floor of the unit and that it was accidental.