Rescuers were monitoring a pod of pilot whales swimming just off the northern tip of New Zealand's South Island late on Tuesday after more than a dozen of the group were killed in a mass stranding.
Rescuers have twice enticed the 28 survivors out to deep water over the past two days after they rebeached themselves and fear the whales could return for a third time overnight. At least 15 whales have died.
Officials said mammal medics and conservation experts would follow the group swimming just off remote Farewell Spit until last light.
"While the whales have come close to shore at times, they remain free-swimming," whale conservation chairy Project Jonah New Zealand said on its Facebook page. "Our staff are staying onsite and will be up at first light to check the beaches."
New Zealand and neighbouring Australia are hotspots for mass whale strandings, owing to large colonies of pilot whales living in the deep oceans surrounding both island nations. Why the stranding occurs is a question that has puzzled marine biologists for years.
Last year nearly 100 pilot whales and bottlenose dolphins died in a mass stranding on the remote Chatham Islands, about 800 km (497 miles) off New Zealand's east coast.
The biggest beaching in modern history was recorded in Australia, also last year, when the majority of a 470-strong pod of pilot whales died after beaching themselves on the country's remote southern coast.
(Reporting by Praveen Menon; Writing by Jane Wardell; Editing by Richard Pullin and David Goodman)
