By Georgina Mitchell
A man has been arrested after a 2-year-old girl was taken to hospital in a critical condition, when she was found unconscious in Sydney's west on Monday afternoon.
Emergency services were called to McCredie Road in Guildford West just before 3.30pm, where they found the girl "unresponsive".
Police said the girl was found inside a parked car after a caller phoned triple zero with a "concern for welfare".
Neighbours told Seven News they heard a woman screaming "you have killed my baby" before emergency services arrived.
Police at a home in Guildford West where a young girl was found "unresponsive".Credit: Seven News
Officers performed CPR on the toddler before she was rushed to Westmead Children's Hospital in a critical condition with a police escort.
A NSW Ambulance spokesman said the young girl was believed to be in cardiac arrest.
Police set up a crime scene at a house on McCredie Road, with another crime scene taped off on nearby Marian Street in Guildford.
A 23-year-old man, who police said was known to the girl, was arrested just before 5pm at Fairfield.
He was taken to Merrylands Police Station where he was said to be "assisting with inquiries".
Police said the circumstances of the incident are not known.
"Investigations are continuing," a NSW Police spokesperson said in a statement.