A man who was hit in the head with a baseball bat has been flown from the NSW north coast to a Sydney hospital in a critical condition.

Police said the 59-year-old man was attacked during a domestic incident at a caravan park on the Pacific Highway in Coffs Harbour at about 2.45am (AEDT) on Friday.

He was flown to Royal North Shore Hospital, where he is in a critical condition on life support.

A 26-year-old man was arrested at a business in South Coffs Harbour at 8am (AEDT) and is currently assisting police.

Anyone with information about the incident who has not yet spoken with police is urged to contact Crime Stoppers on 1800 333 000.