The Farewell Spit beach, at the top of the South Island, is a renowned death trap for whales.
Of the 53 whales in the latest stranding, 13 were dead and efforts were being made to refloat the remaining 40.
Regional department of conservation manager John Mason believes the whales were from the same pod herded out to sea after another stranding during the week.
Farewell Spit, about 150 kilometres (90 miles) from the tourist city of Nelson, is frequently the scene of mass strandings by pilot whales, with scientists unsure why they swim ashore in large groups.