Rescuers cheered as a stranded whale was successfully refloated at Christchurch's Waimairi Beach.

Thousands of locals, Project Jonah volunteers and Department of Conservation (DOC) workers watched nervously as the false killer whale swam out to sea after being refloated on a pontoon about 2.30pm on Sunday.

The whale was one of two discovered stranded on the beach before first light. An adult female, found about 500 metres away from the younger whale, was already dead. It was taken away for burial by the Tūāhuriri Rūnanga on Sunday afternoon.

1 of 11 IAIN MCGREGOR/FAIRFAX NZ A human chain helps move water to the stranded whale on Christchurch's Waimairi Beach. 2 of 11 SAMMY ZHU Two local people help a stranded false killer whale at Waimari Beach early Sunday morning. 3 of 11 SAMMY ZHU A Christchurch local works to save a stranded false killer whale early this morning at Waimari Beach 4 of 11 TINA LAW/FAIRFAX NZ The dead whale on Waimari Beach. 5 of 11 ALDEN WILLIAMS/FAIRFAX NZ Project Jonah volunteers work to keep a stranded whale alive on Waimairi Beach in Christchurch. 6 of 11 ALDEN WILLIAMS/FAIRFAX NZ The stranded whale at Waimairi Beach. 7 of 11 ALDEN WILLIAMS/FAIRFAX NZ Hundreds of people help save a whale stranded on Waimairi Beach on Sunday. 8 of 11 ALDEN WILLIAMS/FAIRFAX NZ Locals transport water up Waimairi Beach, trying to save a stranded whale on Sunday. 9 of 11 ALDEN WILLIAMS/FAIRFAX NZ Locals care for the stranded whale on Waimairi Beach. 10 of 11 ALDEN WILLIAMS / FAIRFAX NZ One of two whale stranded on Waimairi Beach on Sunday. This one sadly did not make it back to sea. 11 of 11 IAIN MCGREGOR/FAIRFAX NZ Dozens help refloat a stranded false killer whale at Christchurch's Waimairi Beach on Sunday.

The living whale was kept alive by Project Jonah volunteers who dug a hole around it to prevent sand from compressing its organs. They kept the whale wet with buckets of water carried by hundreds of locals who formed a human chain to bring water from the ocean.

DOC biodiversity supervisor Craig Alexander said a digger was used to carve out a trench, which allowed the mammal to be refloated earlier than first thought. The rūnanga performed a karakia (prayer) before the whale was refloated.

An inflatable rescue boat from the Waimairi Surf Life Saving Club was then used to steer the whale on the pontoon over the breaking waves and then the Coastguard took over to ferry it out about 500m from shore.

ALDEN WILLIAMS/FAIRFAX NZ The stranded whale at Waimairi Beach.

Alexander said there were a few nervous moments when the whale started to turn sideways going over the breakers but it righted itself again, to everyone's relief.

"The Coastguard was watching it for quite a while until it disappeared and they were not able to find it again. It was diving and showing behaviour that it should."

Alexander said he would pray the whale did not restrand itself overnight. Christchurch City Council rangers would patrol the beach over on Monday and Project Jonah asked people living in the area to keep a close eye on the coast over the next few days and to call them or DOC if they saw anything.

The support from the locals was fantastic, Alexander said, and despite the number of people, everyone was well-behaved and respectful of the whale. Police were called at one stage when two children, aged 6 and 3, went missing, but they were later found.

People came down with buckets to fill with water and food to feed the hungry volunteers.

Tessa Marsden travelled from Kaiapoi with two big pots of soup to hand out.

"We just made some soup and bought it down. It's all gone."

New Brighton resident Leonie Bowkett said she felt compelled to help save the whale.

"I just love animals. I love whales. They need saving and it needs help," she said.

TINA LAW/FAIRFAX NZ The dead whale on Waimari Beach.

Waimairi Beach resident Barbara Whitaker​, who was part of the human chain, said her neighbour told her about the stranding and she rang all her neighbours to come down.

"It's great to see the community in action."

Tasman O'Sullivan, 13, was on the beach at 8am with her family.

SAMMY ZHU Two whales stranded at New Brighton beach on Sunday.

"I was talking to the whale and reassuring it," she said.

Project Jonah volunteer Harvey Bentham said he was relieved to see the whale successfully refloated.

Project Jonah put out a warning on its Facebook page on Saturday afternoon after a pod of whales was spotted about 500m offshore from Port Levy, on Banks Peninsula.

It was not known why the whales stranded but scientists from Otago University would complete tests on the dead whale.

It had been about six years since the last whale stranding in Canterbury, which was at Port Levy, Alexander said.

A post on Project Jonah's Facebook page said it was very rare for false killer whales to get stranded.

"This is only the third ever record of a false killer whale stranding in the South Island with the last one being in 1984."