Treacherous conditions have pummelled the annual Sydney to Hobart yacht race, forcing dozens of withdrawals as Black Jack led a tight battle for line honours.

Sunday's starting fleet of 88 yachts for one of the world's toughest ocean events was cut down to 56 by Monday evening, as competitors peeled off after suffering damage or minor injuries to crew.

A close scrap for line honors was being fought out at the front of the pack between super maxis Black Jack, SHK Scallywag, LawConnect and the slightly shorter 80-foot (24­metre) Stefan Racing.

Black Jack, skippered by Mark Bradford, was race leader as they headed into the Bass Strait.

Cruising Yacht Club of Australia Commodore Noel Cornish said although the conditions had been "very tough," the challenge of a "great adventure" is what drew competitors.

The race leaders were now through the worst of the weather and were expected to arrive in the Hobart by Tuesday afternoon if conditions held, he told media in the Tasmanian capital.

"[The] yachts that are out there now are hunkered in, they're going hard and they're really looking forward to getting down here."

Crowds had turned out to watch the boats race out of Sydney Harbour on Boxing Day after COVID-19 forced the blue-water classic's suspension in 2020.

But the pandemic continued to cause problems.

Before the start, four yachts were forced to retire, leaving 88 entrants at the starting line including 17 two-handed crafts, which are allowed to take part for the first time.

It was a sharp reduction from the 157 boats that set out in 2019.

In a dramatic start to this year's race, a major technical problem cost the 100-foot SHK Scallywag prime position to LawConnect after leading out of the heads.

Numerous withdrawals followed, as southerly winds - which reached 30 knots overnight - whittled the competition down.

Weather is a critical ­factor in the 628-nautical-mile (1,200-kilometer) yacht race down Australia's east coast to Hobart.

Six men died, five boats sank and 55 sailors were rescued during the 1998 event when a deep depression exploded over the fleet in the Bass Strait.

The latest weather update predicted south to southeasterly winds to ease on Monday evening in the Strait and onto Tasmania's coast.

Though the first yacht to reach the finishing line grabs most public attention, the main prize for sailors is regarded as the handicap honors, which take account of the size of the yachts.