The 40ft Jeanne SOLO Sailor sent out a distress signal at 20.23 on Monday from 14 miles from the Sisargas Islands off Spain's northwestern Galicia region, the coast guard said.

A rescue ship carrying five divers set sail to rescue the man, who has not been named, as one of three helicopters sent to aid the search located the upturned vessel as the sun went down.

The man responded to divers seeking signs of life by banging on the hull from the inside.

However at the time the sea was too rough to attempt a rescue, so the team attached buoyancy balloons to the ship's hull to prevent it from sinking further and waited until the morning.

The man was found under the boat wearing a neoprene survival suit submerged in water up to his knees, as two divers swam under to help him out.

He was airlifted to safety and taken to hospital for checks but released soon afterwards with no issues.

Vicente Cobelo, a member of the coastguard's special operations team, told a local station the man voluntarily jumped into the freezing water and swam under the boat to reach the sea's surface.

He said: "Of his own initiative, he got into the water and free dived out, helped by the divers who had to pull him through because it was difficult for him to get out in his suit".

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Tracking data had shown the Jeanne SOLO Sailor had set sail from the Portuguese capital of Lisbon on the morning of the previous day.