Eleven people have been rescued after their waka capsized in Tolaga Bay, north of Gisborne.
They were practising for the upcoming transit of Venus celebrations on Saturday when their double-hulled waka tipped as they tried to get through three-metre swells at the mouth of the Uawa River.
Police say the crew were poorly dressed in tee-shirts and shorts and none were wearing life jackets.
Gisborne Senior Sergeant Maui Aben says most were in the water for more than an hour as they waited to be rescued, and only a small group managed to swim the 500 metres to shore.
Mr Aben says most were suffering from hypothermia when they were rescued.
He says the crew members were stupid to go out in a waka in such big seas, and somebody easily could have died.
Police will be talking to the group about the incident.