The 8-year-old boy who died after falling into a hot pool suffered burns to almost 100 per cent of his body and underwent three major operations before succumbing to his injuries.

Police yesterday launched an investigation into his death, as one of his surgeons revealed how he tried to save the boy's life.

The youngster, believed to be of Kiribati descent, fell into a geothermal pool at Kuirau Park in Rotorua on Boxing Day. He was taken to Rotorua Hospital and then airlifted to the intensive care unit at Auckland's Middlemore Hospital.

He died on Thursday afternoon, surrounded by family.

Middlemore plastic surgeon Richard Wong She helped treat the boy, who has not yet been named.

"We always operated as if he was going to survive," he said.

"We were hoping we could get him through but all along we knew it was an incredibly long shot.

"The die was cast the moment he fell into that hot pool.

"The reason he lasted as long as he did was because he was a fit and healthy boy," said Mr Wong She.

As soon as the boy got to Middlemore he was taken to surgery for life-saving procedures to relieve swelling and breathing problems and restore circulation to the limbs.

"In the second operation this little kid had on Monday, we were working out how severe the burn injury was and whether we could keep this child alive," Mr Wong She said.

"We did another operation on Wednesday where we found that the burn was, as we'd feared, very deep.

"When he was first sent in to Middlemore he was believed to be a 90 per cent burn, and we reassessed him as being a 100 per cent burn."

Mr Wong She said only 4 per cent of the boy's skin could have been used to cover the remainder of his burned body.

"That was the magnitude of what we were dealing with."

He said people with such extensive burns were put straight into an induced coma and on life support.

"The amount of pain relief that these people need is such that it's powerful enough to stop them breathing, hence the need for them to be on a ventilator.

"This little boy never regained consciousness. It wouldn't be fair."

Mr Wong She said the boy's death had had a "terrible" impact on him and the rest of the Middlemore team, which included other plastic surgeons, anaesthetists, intensive care specialists and nurses.

"Yes, it is hard. The particularly hard thing is that I've got to come to work the next day and care for the next person."

Rotorua Mayor Kevin Winters said the whole community was thinking of the boy.

"It's an extremely sad way to end the year and we send our sincerest aroha to the family at this difficult time."