Rotorua police and Maritime New Zealand officials have begun inquiries into the death of an Indian raft-rider, Madhu Shah, 66, from Mumbai.
He was thrown from a raft on the Kaituna River, at Tutea Falls, the highest commercially rafted waterfall in the world, on Tuesday, the Daily Post at Rotorua reported.
Pulled back aboard after a short time in the water, Mr Shah collapsed about 10 minutes later and died at Rotorua Hospital on Thursday.
Detective Sergeant John Wilson of the Rotorua police said police investigations were in the early stages and more information would be gained after a post-mortem examination had been carried out.
Mr Shah was in a raft guided by a man working for local rafting company Kaitiaki Adventures.
A nurse who was also on the river tried to resuscitate the man, along with staff from Kaitiaki Adventures, before he was taken to Rotorua Hospital by St John paramedics.
A co-owner of Kaitiaki Adventures Jason Wright said his sympathy went out to the Shah family.
"We have met with Maritime New Zealand to explain what happened. We are all shaken by his death."
Mr Wright said rafting could be dangerous but his customers understood the risks.
"There was nothing we could do, the ambulance guys told us he had a heart attack."
President of the Rotorua Indian Association Harry Chhagan said members were trying to arrange for his body to be taken back home to India.
Mr Chhagan said the man was with his wife, son, daughter, son-in-law and some friends when at the river.
Maritime New Zealand spokesman Ross Henderson said preliminary inquiries were under way.
"Whether there will be an investigation or not will depend on what information we gather in those inquiries," he said.
This week's death was the third in 16 months to occur following an incident on the Kaituna River. In August 2007, an American tourist, Matthew Stidham, 23, died while kayaking on a piece of river known as Awesome Gorge after getting trapped under a fallen branch.
In January this year, Catherine Farrington, 58, of Turangi, died while on a private sledging trip near Paengaroa.
