Organisers of a round-the-world yacht race say hopes of finding an Adelaide sailor missing in the Southern Ocean are fading because of deteriorating weather conditions.

John Fisher fell overboard late Monday night (Australian time), about 2300 kilometres west of Cape Horn off the coast of Chile.

Mr Fisher – who is a British citizen but lives in Adelaide – was “wearing survival equipment when he went overboard”, race organisers said in a statement.

A search and rescue operation was launched, but organisers of the Volvo Ocean Race have said he is now presumed to be lost at sea.

“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,” Volvo Ocean Race president Richard Brisius said in a statement.

“As sailors and race organisers, losing a crew member at sea is a tragedy we don’t ever want to contemplate.

“We are devastated and our thoughts are with John’s family, friends and teammates.”

Mr Fisher’s team, Sun Hung Kai/Scallywag, had remained in the area to search for the missing crew member.

“Scallywag has thus made the difficult decision to turn downwind and head towards the South American coast, the nearest safe landfall, approximately 1200 nautical miles away,” organisers said.

They said given the strong winds, there was “not an option to divert any of the other six Volvo Ocean Race competitors, who are at least 200 miles further east”.

The race is described by organisers as a “45,000 nautical mile race around the world” and team Scallywag was contesting leg seven, from New Zealand to Brazil, at the time of the incident.

The Maritime Rescue Coordination Centre (MRCC) is continuing to assist with search efforts, race organisers said.

“The MRCC has already requested a ship, nearly 400 nautical miles away, divert to the scene,” organisers said.

“The MRCC continues in attempts to contact other ships that may be able to assist.”

Mr Fisher is a member of the Christies Sailing Club based at Christies Beach in Adelaide’s south, and the club has expressed its concerns on Facebook.

“Our thoughts and prayers go out to Kirsten, Ryan and Amy. No words can express our sympathy and pain,” the club said.

The club has been opened up to other members “that want to be together to support each other at this tragic time”.

A race video posted on YouTube by Team Scallywag shows the intensity of ocean conditions, and features an interview with Mr Fisher and his teammates.

“Not many people come to such remote spots on the planet so it is a weird thing,” he said. “But it’s not something that we dwell too much on to be honest.”

Crew members describe a recent near miss due to an effect known as a Chinese gybe, also called a death roll.

“We’ve tipped it over in the middle of the Southern Ocean in the middle of the night,” skipper David Witt said.

“Skippers in all sorts of boats in any race have got enormous responsibility for the welfare of the people onboard.”

In the same video, crew member Ben Piggott concedes falling overboard in such conditions would most likely be fatal.