A one-year-old child has died after being found unconscious at a home in Sydney's west.
Emergency crews were called to O'Hagon Street in Chester Hill about 3:30pm yesterday.
NSW Police said the baby boy was found unresponsive and paramedics were not able to revive him.
"The cause of death is yet to be determined," they said in a statement.
The ABC understands the child was accidentally left in a hot car.
Temperatures in Sydney's west exceeded 31 degrees Celsius on Sunday afternoon.
At Bankstown, 5 kilometres from Chester Hill, the temperature peaked at 31.9C about 1:30pm.
The boy was believed to be in the care of his grandmother at the time.
Officers have spoken with distraught witnesses at the scene, including a woman who was loaded into an ambulance on a stretcher.
A family friend said the infant was a twin.
"[It's a] very close family," she said.
"The two twins were always together — always together."
The woman said the boy's mother was a good parent with six children.
"I'm in shock, disbelief, heartbroken," she added.
"I just can't believe this has happened."
