George Mostert, 78, was the first on the scene closely followed by two removalists working nearby.
“When I got there, the flames on her clothing were about a metre high,” he said.
“I grabbed a furniture cover and threw it over her to snuff out the flames.”
Mr Mostert said they were unable to save the woman.
“That’s the worst thing I’ve seen in nearly 80 years,” he said.
“I’m still shaken.”
Six fire trucks from Armadale, Hope Valley and Byford responded to the 10.20am emergency call and a small fire in the home was put out within 20 minutes.
Police confirmed that one person was deceased but were not yet able to release further details. Arson squad detectives visited the premises and investigations are continuing.