Wellington - A 31-year-old Japanese sailor is missing, believed dead, after falling overboard from a Japanese whaling ship in Antarctic waters on Monday, news reports said.

New Zealand's Rescue Coordination Centre said it had relayed a mayday message to ships in the area after being asked to help by the Japanese Coastguard, but the request did not come until six hours after the man was missed from the Kyoshin Maru Number Two.

The man was wearing overalls and no life jacket when he disappeared in the Southern Ocean where the water temperature was at the freezing point with 4-metre swells, rescue centre spokesman Mike Roberts told Radio New Zealand.

He said that nobody was likely to survive longer than one hour in those conditions. (dpa)