A homicide investigation is underway following the death of a baby found with critical injuries at a Foxton Beach House

The six-month old was discovered by police on Seabury Avenue last Sunday, and airlifted to Starship Children's Hospital in Auckland.

Detective Senior Sergeant Michael Deegan says they're working to establish when and how the fatal injuries likely occurred.

Police have not said when the baby died.

Horowhenua Mayor Bernie Wanden's described the situation as very sad and tragic.