Man dead, child critical after Perth fire

A man has died and his three-year-old great-grandson is fighting for life after being rescued from a Perth house fire.

The blaze on Rushbrook Way, Thornlie, was reported about 6.15pm on Wednesday.

Firefighters found the boy and his 69-year-old great-grandfather unconscious in a bedroom of the home, but the man was pronounced dead on arrival after the pair were rushed to Fiona Stanley Hospital.

The boy was transferred to Perth Children's Hospital where he remains in a critical condition.

Neighbour "Darren" said he saw the blaze engulf his friend's home.

"It was pretty bad coming through the window - it popped a roller shutter off the front," he told the Seven Network on Thursday.

"I went over there, but I didn't like looking."

He said he had lived opposite his neighbours for many years.

"(They're a) close family, lovely people. It's a tragedy, I don't know what to say."

The arson squad is investigating, with the cause of the fire yet to be determined.