Five people are dead after a boat with 11 on board capsized off Goose Bay in Kaikōura today.
Police described it as an unprecedented and tragic event.
They said the 8.5m boat capsized shortly after 10am today. Six people had been recovered alive, they said.
Police dive squad staff had recovered the bodies.
Sergeant Matt Boyce, of Kaikōura police, said it was an "unprecedented event" and a tragedy and police were supporting those involved.
Police said it appeared the boat collided with something but couldn't comment on if it involved a whale. Earlier in the day Kaikoura's mayor Craig Mackle said he believed the boat had hit a whale.
The passengers were believed to be part of a bird enthusiast group who had hired a charter to areas of interest.
It is believed they had come from all parts of New Zealand.
Police could not say who the charter was operated by. The skipper went to hospital but police do not believe he is injured.
The survivors all went to hospital but have all been discharged. One person sustained minor injuries.
"We are recovering five deceased from the vessel and in the process of identifying them and our next job is to notify their next of kin," police said.
Kaikoura District councillor Lisa Bond said the incident was "incredibly heartbreaking".
A police spokesperson earlier said they were responding to an incident off Goose Bay in Kaikoura in which a boat has reportedly capsized.
A reporter on the shore at Goose Bay said the at 1.45pm he could see three boats, two of which looked to be Coastguard vessels, and four helicopters in the vicinity of the overturned vessel.
The overturned vessel was about 100m from shore.
Two vessels, including one Coastguard vessel, later left the area, but over the afternoon three more had arrived, including one from Whale Watch Kaikoura and Dolphin Encounter.
Occupants of the Coastguard vessel remaining at the scene could be seen talking to occupants of another boat which had just arrived.
At just after 3pm it appeared divers had entered the water next to the overturned boat.
The Whale Watch boat was earlier travelling slowly close to the shore.
Helicopters had come and gone from the area over the course of the afternoon.
The South Bay slipway was earlier closed to the public while police responded.
A reporter at the scene said firefighters were only letting residents who lived in the area through.
A local firefighter said they were assisting police, but not actively involved in the search and rescue operation.
A spokesperson said St John had been notified of an incident in the water at Goose Bay late this morning.
An image on social media shows a number of people on top of the upturned boat, awaiting rescue.
A spokesperson for Kaikōura Kayaks said he understood a whale had hit a vessel this morning.
He understood an emergency response was underway and had seen a helicopter fly into South Bay this morning.
A spokesperson said while the compliance and safety organisation was aware of the incident it was not directly involved in the rescue effort.
However, a maritime investigator was now heading to Kaikoura to determine the cause of today's incident.
With RNZ, ODT and Kaikoura Star