People gather in the water around a stranded pilot whale at Colville Bay in New Zealand on Sunday, Dec. 27. (New Zealand Herald, Steven McNicholl/AP)

Some 125 pilot whales died in New Zealand after getting stranded on beaches over the weekend, and vacationers and conservation workers managed to coax 43 others back out to sea.

Rescuers monitored the survivors as they swam away from Colville Beach on North Island's Coromandel peninsula, and by Monday morning, they were reported well out to sea.

Department of Conservation workers and hundreds of volunteers helped refloat the 43 whales at high tide. The volunteers covered the stranded mammals in sheets and kept them wet through the day.

"Some 63 pilot whales stranded ... but it looks pretty good, we've got 43 live ones," Department of Conservation ranger Steve Bolten said.

He added that the cause of the beachings hadn't been determined, but one of the whales may have been sick, or their sonar may have led them into the shallow harbour and they couldn't find their way out again.

Meanwhile on South Island, 105 stranded long-finned pilot whales died Saturday, conservation officials confirmed on Monday. The Golden Bay biodiversity program's manager, Hans Stoffregen, said they were discovered by a tourist plane pilot and only 30 were alive when conservation workers arrived.

"They were in bad shape. By the time we got there, two-thirds of them had already died. We had to euthanize the rest," he said.

Because the site is part of a nature reserve, the 105 whale carcasses were left to decompose where stranded, Stoffregen said.

Large numbers of whales become stranded on New Zealand's beaches each summer as they pass by on their way to breeding grounds from Antarctic waters. Scientists so far have been unable to explain why whales sometimes become stranded.