PHOENIX -- An elderly woman was killed in a house fire in the north Valley.

Firefighters on the scene

Fire crews were returning from another call at about 6 p.m. Sunday when they spotted smoke pouring from a home in the area of 40th and Dunlap avenues.

Firefighters said the home and back yard were in flames when they arrived on the scene.

"It was very difficult for them to even get inside the front door," said Deputy Chief Elby Bushong of the Phoenix Fire Department. "Once they got inside about 10 feet, they have fire rolling over the top of them. They had to back out and re-attack the fire from the exterior to try to fight their way back into the house."

Crews fought their way through heavy smoke and intense flames to get to the 71-year-old woman trapped inside the home. She reportedly lived there alone.

The woman, whose name has not been released, was in extremely critical condition when she was taken to the hospital. She later died.

No firefighters were hurt.

It's not clear if there were any working smoke detectors inside the house.

The cause of the fire is not known.