A St John Ambulance rushed the male patient, who was in his 40s, to the helicopter.
Clark said the man was "initially in quite a bit of pain".
"He was conscious when he reached us, but he had serious burns to his head and his hands."
The patient had told the rescue team his boat began to sink shortly after the explosion tore through his boat.
He had leapt off the sinking boat into the water and swam to shore.
Clark said the water had a cooling effect on the man's burns. Shortly after he arrived on shore, a local took him into their home and helped soothe his injuries until an ambulance arrived.
Fire and Emergency New Zealand shift manager Murray Bannister said the fire service was first notified of the incident at 6.35pm.
"There was no fire when we arrived on scene - the boat was actually submerged by the time we got here."
Bannister said staffers had reported the boat was moored off a private jetty.
A Greenhithe resident told the Herald they didn't see any smoke or fire from the scene of the explosion.
"We heard and felt the explosion, I thought it was like a cannon going off and it was very loud.
"From the bottom of our garden we were able to hear people calling for help and shouting, and see the scene from one of the nearby wharfs.
"Our neighbours also heard and felt the bang, and they are a bit further away from the location than us."
Clark had told the man he was lucky to be alive.
"With that sort of blast, any sort of explosion, just the sheer forces involved can give you severe traumatic injuries," he said.
"He got off pretty lightly."
