A three-week-old baby boy critically injured in Welcome Bay remains in Auckland's Starship Hospital, as police continue to investigate how the child was injured.

In an earlier statement, Detective Senior Sergeant Greg Turner said a team of 13 police investigators are working on the case but 'are yet to fully determine the circumstances surrounding the boy's injuries”.

He has confirmed that the baby's injuries were not accidental.

The boy's injuries were reported to police after the baby was taken to Tauranga Hospital on Monday, December 31.

He was then flown to Starship Hospital in Auckland.

"The extent of the injuries have shocked the enquiry team and our hearts go out to this child,” says Greg Turner.

'We want to assure the public that Police are working extremely hard to find who is responsible and hold them to account.

"A dedicated team of 13 investigators remains focused on bringing this matter to a conclusion and they have been working around the clock to do so.”

Stuff.co.nz reports that the parents of the baby are a young couple in their 20s, who also have a toddler.

It's understood the couple moved into the Welcome Bay property six months ago.

According to Stuff, a source close to the baby's family says the incident was an 'avoidable tragedy”.

People with information about what happened, and who haven't already spoken with police, can contact Tauranga Police Station on 07 577 4300.

Alternatively, information can also be left anonymously via the Crimestoppers 0800 555 111 line.

-Additional reporting from Stuff.co.nz