More details have emerged about last night's boat emergency off Waiheke Island.

A man was found wrapped in a duvet in the shower, suffering from mild hypothermia and serious burns after he was engulfed in a fireball following an explosion on his boat.

He was rushed to hospital after his boat's engine caught fire near Waiheke Island on Saturday night.

After 10 pm, Coastguard received a distress relay call from a vessel who had been alerted to someone in trouble on a nearby boat.

The vessel in question was moored about 500m from Huruhi Bay when a blaze broke out about 9.45pm.

At 10.20pm, Coastguard volunteer, Chris Griggs, boarded the yacht to find a man wrapped in a duvet in the shower on-board his yacht.

Whilst attending to the man Griggs quickly found out the man had significant burns to his body following an explosion.

"The fire had caused significant burns to his lower body, he had done the right thing in getting wet and sitting under the cold water but in doing so had started to go hypothermic and was in immense pain," Griggs said.

The man explained that an explosion had occurred in the engine room and it quickly became clear that he'd been "engulfed by a fireball whilst exiting the engine room".

The boatie who lived aboard his vessel was attending to some maintenance in his engine room when the incident occurred.

The man was taken to Lion Foundation Rescue and when he was stabilised, was quickly taken by the Coastguard Rescue Vessel to Kennedy Point where they met the Auckland Rescue Helicopter team.

He was taken to the burns unit at Middlemore Hospital.

The Lion Foundation Rescue returned to the boat with firefighters onboard to ensure any hot spots were out.

ASB Rescue stayed nearby overnight with the unaccompanied yacht which has today been looked after by friends of the man.

"Situations like these certainly see your training kick in, it's huge credit to the volunteer crews involved in the incident, we've given the man the best chance of survival in responding how we did and wish him all the best with his recovery."