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The Department of Conservation was first alerted to the mass stranding at the base of Farewell Spit in Golden Bay by a tour operator at 9.30am yesterday.
At around 5.30pm DOC tweeted that said nine of the pod had died while 49 were still alive.
A team of about 65 volunteers, Department of Conservation rangers and Project Jonah experts have been keeping the mammals cool and wet throughout the day.
At about 9.30pm, the refloated whales were swimming about 80 metres offshore from the stranding site.
Conservation staff will check the beach at first light to see whether any have re-stranded overnight.
Project Jonah was taking out a pontoon to try to encourage it to head to sea.
Harvey said it looked as if the whales had never stranded before because they did not bear any marks or abrasions and they were in very good condition.
She said it has been a hot day at the site but DOC staff, Project Jonah members and other volunteers responded quickly and throughout the day the whales had been kept as cool as possible.
Conditions were extremely good for a refloat, she said.
Some volunteers were relieved by others who handled "the wet phase".
"The idea is to group them [the whales] as much as possible together."
Harvey said it was often a female that took the lead.
"The idea is to get them together and let them decide and take it from there."
Boats and spotters were set to follow them until it was dark.
Some volunteers would stay on the beach overnight because it was possible they could strand again in the early morning, Harvey said.
Farewell Spit had been the frequent site for whale strandings and scientists were still trying to work out why.
The last mass pilot whale stranding on Farewell Spit was in February 2017 when an estimated 600-700 whales were beached.
About 250 died while the rest were refloated.