A Norwegian sailboat missing in the Antarctic did not have authorisation for the expedition that appears to have cost three of the five crew members their lives, the Norwegian Polar Institute said Monday.

"They did not receive authorisation from Norwegian authorities," head of the Polar Institute Jan-Gunnar Winther told AFP.

"Without an insurance contract covering possible search and rescue missions, something they did not have, they would not have received our green light if they had asked," he added.

The Berserk, a 48-foot (14-metre) sailboat, has been missing for nearly a week after sending out a distress signal late Tuesday evening from the Ross Sea amid a massive storm, described as the worst in two decades packing winds of up to 180 kilometres per hour (110 miles per hour).

Two of the crew members, Jarle Andhoy and Samuel Massie, had been journeying by quad bike across Antarctica on their way to the South Pole when the tempest struck the boat.

They have been airlifted to New Zealand, where they expressed deep concern for the three crew members who remained onboard -- Norwegians Tom Gisle Bellika, 36, and Robert Skaanes, 34, and and 32-year-old Leonard Banks, a dual South African and British citizen.

The three men, and the ship, remain missing. Only an empty and damaged lifeboat has been found, according to New Zealand rescue workers.

"There's nothing to prove the boat is lost but I am going to be very honest with the family and realistic," Andhoy told reporters in the quake-hit New Zealand city of Christchurch Monday.

Andhoy told Norwegian media he had not sought authorisation for the expedition since "the Antarctic is a no man's land," adding that Norwegian Prime Minister Jens Stoltenberg had "informally" invited him to explore the inhospitable continent.

"It is not the prime minister who gives authorisation for this kind of expedition," Stoltenberg meanwhile told the commercial TV2 News channel.

"It is the specialised authorities. It is the Polar Institute," he added.

New Zealand maritime authorities said Monday the search for the Berserk was continuing but that the anti-whaling ship the Steve Irwin, which had found the life raft, had been released from the operation.