A dead infant was found by a passerby on a beach in Melbourne's south-east on Wednesday afternoon.

The baby, which police believe was a newborn, was discovered at 4.30pm on a beach near the Nepean Highway in Seaford.

Police do not know any details about the circumstances of the death.

They are appealing for the mother to contact police as soon as possible. They hold concerns for the health and welfare of the mother.

Police declined to disclose whether the baby had injuries.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au.