One person is dead after a group of four were swept down the Waikato River when the vessel they were in overturned.
Police were called to Port Waikato near Ngahinapouri Island about 3pm.
The incident happened near Hoods Landing, about 10km south of Waiuku.
Police said three people were taken safely to shore by Coastguard rescuers and were then taken to Middlemore Hospital for treatment.
The fourth person was confirmed dead at the scene.
Police inquiries are continuing. The Fire Service and St John Ambulance also attended the incident.
No further information would be released until next of kin have been advised, police said.
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Meanwhile, further south, a search is underway for a boat on Lake Wakatipu following reports of a distress call.
Southern police communications Shift Inspector Rick Jury said: "We have a search going on as a result of a report by a member of the public that they heard a distress call on the radio channel.''
Mr Dury said Coastguard, a police team and a helicopter were now all involved in the search.
About 4.30pm, a request for a 111 call was issued on an emergency radio channel in the Lake Wakatipu area
.Senior Sergeant Ben Butterfield said police had been unable to contact the person who made the call for help.
"We've tried, heaps," he said.
"That's all that we've been told.
"There's no information about what this person wants 111 for or where they are."
Police appeal for information as to the whereabouts of Black Power member Toa Pitman.