A police investigation is underway after a three-week-old baby was taken to hospital with critical injuries.

Detective Senior Sergeant Andrew Saunders said the baby girl was injured in Hamilton last week.

She is currently in Auckland's Starship Hospital in a critical condition.

Saunders says her injuries are being treated as unexplained while police, alongside Oranga Tamariki, worked to establish the cause.

A scene examination had been completed at the Hamilton home where the baby and her parents lived.

'The investigation is ongoing and further updates will be provided when available,” says Saunders.

-Stuff/Melanie Earley.