New Zealand freediver William Trubridge has broken his own world-record, descending 100 metres below sea level on a single breath of air, only propelled by his arms and legs.

The 30-year-old dived down Dean's Blue Hole on Long Island in the Bahamas this morning, becoming the first to dive a hectometer beneath the sea without weights, fins or other aids.

The famous French diver Jacques Mayol reached this depth in 1980 but used a weighted sled to descend and an inflated lift bag to return to the surface.

Trubridge broke the record on his second attempt of the day, after a bad start on his first try forced him to resurface.

"I entered the water and immediately started shivering. At the end of my breathe-up, as I turned to start the dive, some of the air in my lungs was forced into my mouth, and from there into my stomach. For a split-second I contemplated continuing, but it would have been foolhardy, so I aborted and rolled back onto the surface with a groan of dismay," he said.

Trying again after a short break, his body went into "autopilot" and he has few memories of the dive.

"I remember my depth alarm going off and pulling the tag from the bottom plate, 100 meters below the surface. I remember keeping my eyes half-closed and telling myself to 'relax' and 'flow' as I set off on the long swim back towards the light. And I remember erupting into celebration with my team the moment the judges displayed their white cards"

Freedriving is a dangerous sport and places intense pressure on the body.

"At 100 metres the pressure exerted by overhead water crushes [diver's] lungs to the size of small grapefruit, and the blood vessels inside them swell with blood in order to stop the lungs from imploding. The heart slows to 25 beats per minute, and [diver's] have to fight the narcotic effects of pressurised carbon dioxide and nitrogen - the so-called 'rapture of the deep' that tempts him towards a fateful sleep," said Joy Cottle from AIDA NZ, the body representing New Zealand freedivers.

Trubridge had already broken the record the day before, but was disqualified by the judges for breaching the rules.

"Yesterday I had already touched the mark and come back cleanly, but a technicality (not taking my noseclip off during the surface protocol at the end of the dive) meant that the dive was disqualified," he said.

It was Trubridge's 13th world-record.

He set his first record of 80 metres four years ago and since then has singlehandedly raised the world-record from 80 to 100 metres.

He dedicated today's dive to New Zealand's Hector's Dolphin, which is currently in danger of becoming extinct.

Trubridge, 30, grew up in Havelock North, but sailed the Atlantic, Caribbean and Pacific Ocean with his parents.

By age eight he was already diving to a depth of 15 metres.

Trubridge rediscovered free-diving when he was 22 and has spent hours a day underwater since then.