A 43-year-old man has been charged after allegedly dousing three children in lighter fluid and setting one of them on fire in the Perth suburb of Doubleview.
Police were called to a disturbance in Holbeck Street shortly after midnight, where officers were told a man had poured flammable liquid inside a house and three children had been burned.
An off-duty officer who is believed to live on the street intervened, placing them in a bathtub in the house.
It is believed the officer then took the children to another residence to provide first aid.
One of the children, a four-year-old girl, suffered extensive burns and is in a critical but stable condition at Princess Margaret Hospital (PMH).
It is understood she had been lying in a cot at the time of the incident.
A seven-year-old girl who also suffered burns is in a stable condition in PMH.
Police said a six-year-old boy was with family.
A 43-year-old man, who is believed to be the father of the children, has been charged with one count of aggravated grievous bodily harm and two counts of attempted grievous bodily harm.
He is due to appear in the Perth Magistrates Court.
Police said the investigation was ongoing and further charges were expected.
Holbeck Street was cordoned off from the public overnight, and several areas were being examined by forensic officers.
The house was not badly damaged