Police have found the body of a four-year-old girl at the scene of a house fire at Claymore in Sydney's south west.
Emergency services were called to the two-level townhouse on Duterreau Way at Claymore shortly before 2.30pm (AEDT).
A woman managed to escape the blaze with one of her twin daughters but told police she believed the other child was still inside the house.
NSW Police confirmed in a statement on its website that a child's body had been found.
"Initial inquiries suggest the girl's mother smelt smoke coming from an upstairs bedroom and went to investigate," the statement said.
"The woman was able to retrieve one of her two children but was forced back by the flames.
"A report is being prepared for the coroner."
A highway patrol officer had also tried to enter the house but was pushed back by the blaze and had to be treated for smoke inhalation.
Ian Krimmer from Fire and Rescue says crews could only reach the girl's body once they had put out the blaze.
"Our crews were here within five minutes of the call, a very rapid response," he said.
"They immediately attempted a rescue but the fire was just too fierce, the roof was collapsing around them, they just had to withdraw.
"Sadly one young girl has died as a result of the incident."
The woman and the surviving child were taken to Liverpool Hospital for further medical checks.
Mr Krimmer says it is unclear what started the fire.
"It's much too early to say how this fire has started, it's caused enormous damage, the roof has collapsed, our investigators are on scene," he said.
"Whether they can come up with any determination this afternoon is yet to be found out, it will take some time."