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.
Police are now working through the formal identification process.
Sergeant Matt Boyce 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.
Asked if it was a working theory that the boat hit a whale, police said they were speaking to a number of people to find out what had happened.
Whales were resident and had been seen in the area, Mackle said. Sea conditions at the time were "perfect, flat", he said.
The passengers were believed to be part of a bird enthusiast group who hired a charter boat to visit 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.
Mackle said it was a tragic event that impacted many lives.
He thanked everyone involved in the recovery.
Being able to bring everyone home "is the best result" in such a tragic situation.
"There's nothing worse for a family to not have that closure, to return the deceased to the family, will be special for them," police said.
Everyone who could have been involved helped out where they could.
Asked if the boat was overloaded, Mackle said he couldn't answer that.
The bodies of the dead were found in the vessel.
The coastguard said it was a "tragic operation".
"Our thoughts go out to friends and family of the deceased," the coastguard said.
Tracy Phillips, Maritime NZ Principal Investigator, said the organisation had sent two investigators from Christchurch to Kaikoura.
"Any investigation activity will commence only after rescue/recovery operations have concluded. We'll be conducting a thorough investigation under the Health and Safety at Work Act and the Maritime Transport Act and we'll do everything we can to support NZ Police in their investigation."
Mackle earlier said he felt sick as the incident unfolded.
Richard Hill from Cods and Crays fish and chip shop told RNZ he had worked with the skipper on the boat before.
"He's a very safe man, there's no way he'd take any risks. So there's just got to be something sort of a freak of nature, I would have thought. A very sad day for Kaikōura really, just a shock," Hill said.
Kaikoura District councillor Lisa Bond said the incident was "incredibly heartbreaking".
The South Bay slipway was closed to the public while police responded.
A reporter on the shore at Goose Bay said 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.
Two of the helicopters in the air appeared to be Westpac Rescue helicopters.
A St John spokesperson said they had been notified of an incident in the water at Goose Bay late this morning.
The spokesperson said police were in charge of the emergency.
An image on social media showed a number of people on top of the upturned boat, awaiting rescue.
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