A Superior duplex is likely a total loss following a fire that started around noon Sunday, but no one was injured, according to officials.

Firefighters had the blaze mostly out, but were continuing to work on hotspots Sunday afternoon, according to Rocky Mountain Fire spokeswoman Michelle Kelly.

"We're still determining cause and origin," she said.

One family was home at the time, but got out safely, according to Boulder County sheriff's Sgt. Lance Enholm. The second family came home, possibly after a camping trip, to find the house on fire. Enholm said two dogs also died in the fire, while a cat is unaccounted for.

A neighbor called in the fire Sunday after seeing flames on the outside of the building, he said, and  firefighters found the fire going strong when they arrived.

Along with Rocky Mountain Fire and the Boulder County Sheriff's Office, Lafayette, Louisville, Boulder Rural, Longmont and North Metro fire departments responded.

Kelly, of Rocky Mountain Fire, said a large number of firefighters were needed in part because the day was so hot, making it necessary for teams of firefighters to take short turns inside the house to avoid overheating.

While the residents likely can salvage some belongings, she said, there's too much structural damage to the red brick house with green trim for it to be livable.

There's significant roof damage," she said.

The Red Cross is helping the residents with their housing needs.