Police are continuing to investigate the death of a three year-old boy at his home in the Perth suburb of Hilton.

Yesterday afternoon, the boy's 24 year-old mother made a frantic phone call to St John Ambulance service saying her son had serious injuries.

Detective Senior Sergeant Doug Nelson says the ambulance took the boy to Fremantle.

"The boy was conveyed to Fremantle Hospital because of his injuries and unfortunately we're advised that he's now deceased," he said.

"There are circumstances surrounding that death that are currently under inquiry."

Police interviewed the mother last night and say they are still trying to ascertain how the boy was injured.

Police are refusing to confirm earlier reports that the boy had been found in a washing machine.