An injured New Zealand scientist is in a stable condition today after a five-hour 1000km mercy flight from remote Raoul Island.

GNS Science technician Andrew Cowie, 31, is believed to have smashed ribs on Friday afternoon when he he fell out of boat while working on installing tsunami and volcano warning systems to the ocean floor.

"There were quite big swells, I understand," said GNS spokesman John Callan. "He was either getting in or out of the boat when he lost his balance and fell."

Mr Cowie spent an uncomfortable night at the Department of Conservation's medical facility because the Phillips rescue helicopter couldn't land in the dark on Raoul Island part of the Kermadec group halfway between New Zealand and Tonga.

The chopper picked up him and a DOC volunteer doctor up yesterday morning and flew back to the mainland arriving at Tauranga Hospital at 3pm.

Mr Cowie was met by his wife Sarah Marr and 14-month-old son James from Featherston in the Wairarapa.

Ms Marr, a pharmacist, said doctors suspected Cowie had broken ribs.

"He's in a bit of pain, but he's happy, talking and making jokes. He's very disappointed because he would have liked to see the project all completed," she said last night.

A Tauranga Hospital spokeswoman said this morning that Mr Cowie was in a stable condition.

The Kermadecs are subject to frequent volcanic activity.

Yesterday a powerful 6.7-magnitude earthquake struck 270km to the southwest, but there were no reports of any damage.

In March 2006, DOC worker Mark Kearney, 33, died after Raoul Island's Green Lake erupted.