A 64-year-old man is fighting for his life in hospital after being stabbed in the neck and head early on New Year's Day at Waihi Beach.
Police say the man and his wife are New Zealanders, who live in Australia and were holidaying in a caravan at the Bay of Plenty resort.
Detective Inspector Karl Thornton says the couple heard a disturbance about 1am and went to investigate.
"They have encountered a man and told him to leave, but then the husband has suffered stab wounds to his neck and head before the offender has fled."
The victim was flown by helicopter to Waikato Hospital, where he was said on Tuesday night to be in a critical condition in the intensive care unit.
Waikato police spokesman Andrew McAlley told NZ Newswire that forensic teams were working into the night at the scene where the caravan was parked and officers were canvassing the area.
"We are taking advantage of the long sunlight hours, he said.
Det Insp Thornton said earlier that there were a lot of people in the area celebrating the New Year and police hoped someone might be able to identify the offender.