A boatie who was thrown from a powerboat after it collided with a buoy was too dazed to tell emergency services that his mate was trapped under the capsized vessel.

The passenger on the 5.6m runabout died after the boat struck a channel marker buoy near Matakana Island, northwest of Mount Maunganui, about 1.50pm yesterday. It is understood the man who died was a Canadian tourist in his 60s.

The 65-year-old skipper was taken to Tauranga Hospital with lacerations to his face and serious injuries.

Immediately after the collision a boatie in a nearby yacht named Wind Rose put out a mayday signal and tethered the yacht to the upturned boat.

Harbour warden Brian Rogers, who was third on the scene after responding to the call, said rescuers were not immediately aware of how many people were involved in the collision.

"There was initially some confusion ... [the rescued man] was clearly dazed and confused so the searchers weren't sure whether they were looking for a second person or not.

"He was in shock, understandably, so he wasn't very coherent."

A crewman from the Port of Tauranga pilot boat dived under the capsized hull and emerged with an unconscious body.

Mr Rogers pulled the man on to his vessel and, with a colleague, performed CPR on him for 10 minutes.

"Then the coastguard told us to stop. He'd been under the water for 20 minutes and had a massive head injury. I don't think there was anything that could be done for him."

He said the seriousness of the injuries suggested the pair had been travelling at a high speed.

"They must have smacked [the buoy] at a really good rate of knots."

The incident occurred on open water where there is no speed limit. The cone-shaped marker buoys, made of wood and metal, stand 3m above the surface at 100m intervals.

Local iwi have placed a rahui on Tauranga Harbour for the next three days.

Tauranga Coast Guard operations manager Simon Baker said they arrived as quickly as possible but could not save the Canadian tourist.

"I've never gone to anything quite like this in my lifetime ... By the time we got there, there wasn't anything we could do. We arrived after he was out of the water and was already deceased."

Everyone at the scene was trying to save the two men, Mr Baker said.

"It was quite sombre out there, but everyone was pitching in and doing what needed to be done."

He said the conditions were calm with very little wind and the accident happened because the skipper was not paying attention.

"It's just a case of maintaining a proper lookout when travelling, that's just one of the golden rules of travelling in a boat."

Mr Baker believed the two men were returning to Tauranga after a fishing trip in the harbour.

Tauranga police said they were still informing the dead man's next of kin and that his death had been referred to the coroner. Authorities towed the boat back to Sulphur Point Marina.

Police are appealing for any witnesses to contact the Tauranga Police Station on (07) 5774300.