Rival supermaxis LDV Comanche and Wild Oats XI were in a fierce battle to the finish line Wednesday, exchanging the lead several times as they stayed on course to smash the Sydney to Hobart race record by several hours.

The epic contest between the duelling 100-footers has marked this year's 628-nautical mile (1,163-kilometre) bluewater classic, regarded as one of the toughest yacht races in the world.

Comanche had rounded the Tasman Island and was expected to cross the finish line after 9.00pm local time (1000 GMT) Wednesday, well inside the record time of 1 day 13hr 31min 20sec set last year.

Wild Oats was just two miles behind, race organisers said.

The supermaxis had sailed down the Tasmanian east coast at 20-30 knots before a strong north-easterly wind in what organisers describe as an "astonishingly fast race".

"It's something quite extraordinary when you find that the race record in these days is beaten by five hours, as it was last year," Cruising Yacht Club of Australia commodore John Markos told reporters earlier Wednesday.

"We were all pretty staggered that the race (record) was so comprehensively beaten, and to find that the very next year that you've got the potential to beat it by several more hours is really extraordinary."

Of the 103 competitors, three yachts -- the German TP52 Rockall, Sydney yacht Wots Next and Queensland vessel Opt2Go Scamp -- have retired from the race marked by ideal sailing conditions.

The dash to Hobart's Constitution Dock could be delayed on the notoriously sluggish Derwent River before the finish.

"The good news is that the Bureau of Meteorology is forecasting a continuing north-easterly in the river tonight, which, while not from a favourable direction, at least represents continuing wind," the organisers said.

- Crucial protest? -

This is the strongest line-up of supermaxis to contest the Sydney to Hobart, with all four having won line honours in previous races.

Eight-time winner Wild Oats had earlier closed the gap to Comanche while as she sailed "bare-headed" -- mainsail-only -- for some time after damaging the topsail, which is suited to the conditions.

But if Wild Oats finishes ahead of Comanche, a formal protest could play a crucial role in determining the winner.

Comanche indicated Tuesday she would file a complaint -- which could result in a minimum five-minutes penalty -- after the two super-yachts almost collided early in the race when Wild Oats appeared to tack too close.

The protest has to be lodged within six hours after Comanche crosses the finish line, with an international jury to hear the evidence after the race, Markos said.

Chasing the leaders were fellow supermaxis Black Jack and InfoTrack, which broke the race record last year under the name Perpetual Loyal.

Hong Kong businessman Karl Kwok's 80-footer Beau Geste was fifth ahead of last year's overall winner, Giacomo, now racing as Wizard.

In the race for the Tattersall Cup (overall winner) -- the handicap honour for the vessel that performs best according to size -- Matt Allen's new TP52 Ichi Ban was leading the charge ahead of Wizard.

Source: AFP