A three-year-old boy has died and a two-year-old is in a stable condition after two separate backyard pool incidents in Sydney.

The three-year-old is believed to have collapsed after getting out of a backyard pool at Riverwood on Sunday night.

Emergency services found the boy unconscious around 5.30pm and he was rushed to Sydney Children’s Hospital in a critical condition, but died a short time later.

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“It is still under investigation and it will be for the coroner to determine how he died,” a NSW police spokeswoman told AAP.

Police were unable to confirm reports the boy had a pre-existing condition.

An hour later paramedics were called to a Camden South home after a two-year-old boy was pulled from a backyard pool.

He was airlifted to The Children’s Hospital at Westmead in a critical condition but has reportedly regained consciousness and is in a stable condition and expected to make a full recovery.

Police could not confirm reports of a faulty gate at the Camden South property.