BENTONVILLE, Ark. (AP) — A fire possibly caused by a space heater swept through a home early Tuesday, killing five children on the second floor after their parents were unable to reach them through the smoke and flames, authorities said.

The children's parents were awakened in a downstairs bedroom by a smoke alarm around 1 a.m., but escaped without injury, investigators said.

Fire Chief Dan White said the staircase in the 1 1/2-floor home was so narrow he had to turn sideways to get through to the second floor.

The cause of the blaze was under investigation.