London: An Adelaide-based British Volvo Ocean Race crew member who fell overboard in the Southern Ocean is presumed lost at sea, organisers said on Tuesday.

John Fisher, 47, had been competing with Hong Kong entry Team Sun Hung Kai/Scallywag on leg seven of the race from Auckland to Itajai in Brazil and was reported missing in extremely rough seas on Monday.

The 65-foot (19 metres) yacht's location was some 1400 nautical miles (2600 km) west of Cape Horn, and 1200 miles from the nearest safe landfall in South America. The nearest competitors were 200 miles away downwind.

Fisher, a Sydney-Hobart veteran who was born in Southampton but based in Adelaide, had been on watch and was wearing appropriate survival gear.

"Given the cold water temperature and the extreme sea state, along with the time that has now passed since he went overboard, we must now presume that John has been lost at sea," race president Richard Brisius said in a statement.