Police are urgently searching for a Hunter man who disappeared after leaving a medical facility with a serious stomach wound.

Peter Bates, 42, was last seen leaving a hospital in New Lambton Heights and boarding a bus about 3pm on Thursday.

Authorities say there are grave concerns for his welfare, with Peter requiring urgent medical treatment for the injury.

The circumstances surrounding the wound remain a mystery, with police confirming the cause is not yet known.

After he failed to return home and could not be contacted, officers from Newcastle City Police District launched an investigation to find him.

Peter is described as being of Caucasian appearance, about 175cm tall, with a medium build and short brown hair. He was last seen wearing a grey beanie, black hoodie, light grey track pants and red shoes, while carrying a white plastic bag.

He is known to frequent the Newcastle and Lake Macquarie areas.

Anyone who has seen Peter or knows of his whereabouts is urged to contact Crime Stoppers immediately on 1800 333 000.