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. 

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. 

The passengers were believed to be part of a bird enthusiast group who hired a charter boat to visit to areas of interest. 

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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. 

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. 

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. 

Everyone who could got involved and helped out where they could. 

Asked if the boat was overloaded, Mackle said he couldn't answer that. 

The bodies are those dead were found in the vessel. 

The coastguard said it was "tragic operation". 

"Out thoughts go out to friends and family of the deceased," the coastguard said. 

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. 

Photos of the rescue at Goose Bay. Photo / supplied 

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. 

A person on top of the vessel during the rescue operation. Photo / supplied 

Maritime New Zealand is sending an investigator to the region in the wake of the unfolding tragedy. 

A spokesperson said while the compliance and safety organisation was aware of the incident it was not directly involved in the rescue effort. 

A maritime investigator was heading to Kaikoura to determine the cause of today's incident. 

- additional reporting RNZ