According to the local broadcaster RNZ, Kaikoura mayor Craig Mackle said earlier that he believed the vessel had collided with a whale. Police have not yet confirmed the cause of the deadly incident.
The boat, reportedly carrying 11 people from a bird enthusiasts group, tipped over at around 10 a.m. on Saturday (22:00 GMT on Friday).
Search and rescue operations have reportedly been completed and the five bodies were retrieved from inside the boat. Police are now working to formally identify them. Six survivors, including the skipper, were rescued, the RNZ reported.