Defending champion Mathieu Van Der Poel and his eternal rival Wout Van Aert will be the centre of attention in a star-studded cast at Sunday's Tour of Flanders, arguably the toughest one-day bike race on cycling's World Tour.

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Embarking from Antwerp mid-morning the riders cover 254km and 19 storied hills before arriving at Oudenaarde six hours later, where 2016 champion Peter Sagan said Friday the strongest man on the day always wins.

The race is a major event in Belgium and would normally attract crowds way in excess of a million, but Covid-19 restrictions mean the 105th edition will have no roadside fans.

In 2020 Van der Poel and Van Aert, both 26 and who have contested races with each-other since childhood, came round the last corner elbow-to-elbow in a breath-taking finale decided by centimetres on the line after an interminable struggle down the home straight.

"I'm not on top form," Van der Poel said Friday. "But last year I was ill in the week before the race, and that fact I have already won it once gives me great confidence," said the Dutchman.

Van Aert was keeping his cards close to his chest.

"I'm one of the favourites, but not the big favourite," said the Jumbo-Visma star.

There is a third man seeking a settling of accounts in French world champion Julian Alaphilippe, who hit the tarmac at high speed when a motorbike stopped in front of him during the 2020 edition.

The swashbuckling Alaphilippe also has the advantage of riding for the powerful Belgian team Deceuninck Quick-Step, who will have several irons in the fire Sunday, and may even use their totem as a foil for another man.

"We have a strong team sure, but we have to be really smart, and we have to finish strongly, believe me, this is a tough race," said Alaphilippe, who dismissed any feelings of revenge over the accident that ended his 2020 campaign.

The trio make up the most exciting set of one-day specialists to have emerged in decades, but with such a glittering prize at stake, others will certainly try their luck.

"Anything can happen at anytime on a Tour of Flanders. Danger lurks around every corner. You can't mess around on this race, it's 260km of serious road. Of the 180 contestants 30 will fall and 50 will ride themselves into the ground before the finish," said Belgian Oliver Naesen, of the AG2R team.

"We should fear nobody and count on ourselves, bank on our strengths," said Quick-Step boss Patrick Lefevere, who has taken the title four times in his tenure.