The home where a nine-month-old girl was found dead yesterday remains taped off as police investigate what happened to the baby.

Her parents called triple-0 but when emergency services arrived at the house in Doonside, in Sydney’s west at 10am the child was unresponsive.

She was unable to be revived and her death is being treated as suspicious.

Doonside baby death
The home remains a crime scene as police investigate how the baby girl died. (9News)

Police have spoken to the baby’s parents who are cooperating, and investigators are back on the scene today.

Neighbours said the family moved in about two years ago.

The investigation is ongoing.