Police launch major probe into the mystery death of a toddler found dying in his home in NSW

Police are investigating the death of a four-month-old baby boy who died in hospital after what was described as an 'incident'.

The child was originally taken to Gunnedah Hospital in north-central NSW on Tuesday, where police were informed of his injuries.

After being taken to John Hunter Hospital in Newcastle, the child died that evening.

Police have set up Strike Force Monier to investigate the boy's death.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or Gunnedah Police Station on 02 6742 9099.

The four-month-old boy died at John Hunter Hospital in Newcastle on Tuesday (pictured).