A 20-year-old crew member suffered a serious spinal injury in "traumatic event" aboard a cruise ship close to Cook Strait.
The incident happened on the Legend of the Seas, which was travelling up the east coast of the South Island and through Cook Strait on its way to Brisbane overnight on Wednesday, a Maritime New Zealand spokesman said.
A Life Flight Westpac rescue helicopter was called to the scene, about 32 kilometres southeast of Cape Campbell, at the southern end of Clifford Bay, near Blenheim, at 12.30am.
The woman, who suffered a lower back fracture, was winched from the ship by a team using night-vision goggles, and was flown to Wellington Hospital in a serious but stable condition.
"Our crew member required urgent medical attention that can only be provided in a hospital.
"In an effort to provide her with medical care as quickly as possible, we contacted authorities and requested a medical evacuation by helicopter," it said.
"We are keeping our colleague in our thoughts and prayers for a speedy recovery."
The company's New Zealand spokeswoman, Pauline Ray, said she could not comment on how the accident occurred or whether an investigation was likely.
Wellington Hospital said on Thursday afternoon that the woman was in a stable condition.
Life Flight crewman Mike Beausoleil said the rescue operation was undertaken in trying conditions, with the response team using night-vision goggles while trying to winch the injured woman from the moving ship.
She was stabilised by a medic who had been winched down to the ship's deck, and was eventually flown to hospital at 2.30am.
It took about 20 minutes to lift her off the ship.
"Night-winching on a moving vessel is about as difficult as you can get," Beausoleil said.
A WorkSafe NZ spokesman said that, under the Health and Safety at Work Act, it investigated only those incidents involving New Zealand boats, or New Zealand-based charter boats hired by foreign operators when used in the country's waters.
Legend of the Seas, which is based in the Asia-Pacific region and registered in the Bahamas, is not covered by the act.
It is sailing a 14-night New Zealand tour and is due to arrive in Brisbane on Sunday.