Child, great-grandfather killed in WA fire

A Perth family is mourning a four-year-old boy and his 69-year-old great-grandfather, killed in a house fire.

Hugo Alaniz, 69, was pronounced dead on arrival at Fiona Stanley Hospital on Wednesday while Thyreese died at Perth Children's Hospital on Thursday.

The blaze on Rushbrook Way, Thornlie, was reported about 6.15pm on Wednesday and firefighters rescued the pair from a bedroom.

Inspector Dean Snashall told reporters at the scene the pair was unresponsive when police and firefighters arrived.

Police confirmed the child's death about 5pm on Thursday, but family had already told reporters arrangements were being made to donate his organs.

"He's going to live through someone else," Raul Alaniz told the Seven Network on Thursday.

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

Police will prepare a report for the coroner.