SYDNEY — Race favorite Comanche snatched the lead after a slow start in the grueling Sydney-Hobart on Thursday, as more than 150 yachts sailed into open ocean for the annual race down Australia's east coast.

Supermaxi Infotrack earlier led the boats out of Sydney Heads just hours after skipper Christian Beck played down his yacht's chances, saying victory appeared unlikely unless "someone (else) has a problem".

But 100-footer Comanche, which holds the race record, soon left behind four other supermaxis including the crew of Wild Oats XI, who were fighting hard to defend their 2018 title.

Wild Oats XI tactician Iain Murray declared the recently repaired boat "100 percent ready to go" after it sustained mast and deck damage last month.

"Comanche is one extreme, and we are the other extreme," he said ahead of the race start.

"The skinny little boat likes some light breeze going downwind, and the bigger boats like to reach.

"I'm sure there's going to be a bit of cat and mouse in all this."

Thousands of spectators lined the harbor shore to watch as the boats jostled to secure a favorable position for the deep-water classic, aided by 15-knot north-easterly winds.

After weeks shrouded in bushfire smoke haze that forced the cancellation of the Big Boat Challenge, an event that foreshadows the Sydney-Hobart, the 75th race began under clear blue summer skies.

Light bushfire smoke is forecast over the ocean in the coming days, but Cruising Yacht Club of Australia Commodore Phil Billingham said the impact was expected to be "minimal" as many of the boats will be up to 40 miles offshore.

A mild southerly change is expected late Wednesday, with varying winds are forecast throughout the 628-nautical-mile race.

The front-runners are likely to enjoy relatively calm passage across the Bass Strait but the back end of the fleet will face tougher conditions amid increasing winds and thunderstorms expected early next week.

Mark Bradford, skipper of 2018 runner-up Black Jack, was among those predicting a slow race, tipping a line honors-winning time of around one day and 20 hours -- about 11 hours outside Comanche's 2017 race record.

"We'll be a candidate for sure. We've put a huge effort in this year so hopefully we'll reap the rewards," he said.

Billingham said the variable conditions mean the race is wide open for the handicap honors, which goes to the vessel that performs best according to size and was last year claimed by the 66-foot Tasmanian yacht Alive.

"There is a view going around that some of the 60 footers could go very well. It depends when the southerly comes through," he told national broadcaster ABC.

"When they are going down the coast of Tasmania, it will slow them down. They are going into the wind rather than running with it."

Other contenders for the overall handicap win include 2017 champion Ichi Ban as well as TP52 Celestial, he said. — AFP