Authorities should have recognised that a teenage father who bashed his newborn son at a regional WA hospital suffered from fetal alcohol syndrome and restricted his access to the baby, the Coroner has found.

The boy, who cannot be identified, was left alone with his 25-day-old baby son in a room at Bunbury Regional Hospital for the first time in February 2014.

Bunbury Regional Hospital. Credit:Bunbury Mail

Within minutes, he bashed his son's head against a door frame or wall at the hospital.

The baby suffered two fractures to his skull and when staff realised the extent of his injuries, he was rushed to Princess Margaret Hospital for treatment. He died from his injuries nine days later.