The couple, a 19-year-old man and 18-year-old woman, were able to get away from their attackers and summon police, the New Zealand Herald reported. Officers who arrived a few minutes later found people ransacking the couple's tent.
Four people have been arrested, and police were searching for a fifth suspect.
Police said they had been deluged with calls from New Zealanders wanting to assist the couple.
"This is an appalling and mindless attack on a young couple and incredibly sad that this will be their lasting memory of Christmas in our beautiful country,'' Area Commander Inspector Sandra Venables said.
Whakatane is a sizable town in the Bay of Plenty region on the North Island.