A group of 22 pilot whales died Thursday when they re-stranded on a New Zealand beach less than a day after rescuers had shepherded them back out to sea, officials said.

The whales, part of a larger pod that beached on Tuesday, came ashore at Ohiwa Harbour in the Bay of Plenty early Thursday, the Department of Conservation said.

The department, which originally said the group had 21 whales, said 14 of them died and the rest were euthanised on welfare grounds.

It brings the total number of pilot whale deaths in the North Island harbour to 58 since Tuesday.

Darren Grover, from whale rescue volunteer group Project Jonah, said hopes the whales would head to deeper waters after being re-floated on Wednesday proved futile.

"This is a sad outcome after yesterday's successes," he said.

"It's worth remembering that every moment out of their natural environment is a highly stressful time for these beautiful animals."

Mass pilot whale strandings are common in New Zealand, with scientists unclear about why the marine mammals swim ashore in large groups.