Two young boys playing at Maroubra beach found the decomposed body in the sand yesterday morning, a week after another baby was found barely alive in a drain in western Sydney.
New South Wales state police commissioner Andrew Scipione urged the mother of the dead child to come forward.
"Come and talk to us, seek some advice, we need to talk with you," he said, while also pleading with anyone who thought they might know something to speak to authorities.
The naked baby's body was found buried about 30 centimetres (12 inches) in the sand.
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Police said yesterday, it was not known whether it had been stillborn or how it had died.
Its sex was not immediately obvious due to decomposition but a post-mortem revealed today it was a girl, police said.
There were no further details on how the child died or how
long she had been in the sand.
Passers-by were able to rescue the newborn after hearing his cries, and a 30-year-old woman was later charged with attempted murder.
New South Wales Police Minister Stuart Ayres said the cases raised the question of what could be done to help desperate families.
"There is no doubt we find ourselves with two cases that are currently under investigation that requires us to think seriously about what we need to help families that are in crisis," he said.