"The young girl would have ran about 2km and it's all rocky," he said.
"The other chap, who was the skipper of the boat, he did 20 minutes trying to resuscitate the patient."
He said the girl ran until she reached the nearest house with a phone.
"It would've taken a fair while for her to get there, maybe not quite an hour but a while."
A rescue operation involving local boats, the Coastguard and rescue helicopters from Hawkes Bay and Gisborne was launched. Investigations had now begun to establish how the accident occurred, police said.
A St John spokeswoman said the ambulance service had gone in by four-wheel drive and treated a patient at the scene.
An ECT Rescue Helicopter spokeswoman said a helicopter was dispatched, but had since returned to Gisborne.
"The rescue helicopter was immediately dispatched ... and when he arrived there was CPR in progress."
The Lowe Corporation Rescue Helicopter crew also responded to the incident but said no one was airlifted by rescue helicopter.
A spokeswoman from Coastguard New Zealand said the Gisborne Coastguard unit was contacted by police for a search operation, but then stood down.
Today's tragedy was the second fatal boating incident to hit Mahia in the last month.
On October 16, Mahia local Malcolm Blake, 57, died, after the boat he was on flipped. The three other people on board survived.