The Tour de France rolled out of the Atlantic port of Brest on Saturday, 24 teams of eight riders embarking on a 21-day trek across France with all eyes on defending champion Tadej Pogacar and a dramatic day of action assured on the opening stage.

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Large, festive and unmasked crowds had gathered in Brest's industrial port zone for the official start and many were waving the regional black and white flag of Brittany, in this independently-minded corner of France which inspired the comic strip Asterix the Gaul.

On a cool day under grey skies the 197km first stage makes two loops between Brest and Landernau and ends around 1515 GMT with a climb that should leave Pogacar, or at least one of his chief rivals, with a first-day advantage.

This potential bonus means all the top favourites, such as Pogacar, Geraint Thomas and Primoz Roglic, will be forced to vie for position and struggle up the hill.

The same goes for the men best suited to the terrain: world champion Julian Alaphilippe of France, Slovak star Peter Sagan and much-awaited rookie Mathieu Van Der Poel.

Dutchman Van der Poel is given hero status in France having vowed to get the yellow jersey his grandfather, France's revered nearly man Raymond Poulidor, never managed in his own storied career.

Van der Poel was given a raucous reception in Brest at the team presentation on Thursday.

'Something will happen to somebody' 

With a 10 seconds bonus at the stage 1 summit finish line atop a tough 3km climb, followed by an even more extreme version of this trap on stage 2's storied 'Mur (wall) de Bretagne' climb, anyone not yet fully primed will pay the price.

"Something will happen to somebody as it always does," said Geraint Thomas, the nominal head of a quartet of Ineos overall title hopes.

"Four could quickly become three. It will be stressful in the wind and it could be a chaotic first week overall," the Welshman said, with bad weather and grey skies forecast for the opening week.

The race left Brest at 12:30 local time (1030 GMT) after much wrangling followed original hosts Copenhagen pulling out until next year.

Four-time winner Chris Froome is back at the Tour although out of the leadership roles, and suggested a clutch of the main favourites would be tough to beat.

"Tadej Pogacar isn't slowing down, is he?" Froome said of the defending champion.

"Primoz Roglic is really strong and has a good team around him while Ineos has multiple leaders," Froome pointed out.

The four Brittany stages will be followed by a 26km individual time-trial before the race heads through the chateau-littered Loire Valley.

As it reaches the Alps the knives will likely come out for Pogacar.

"The one thing we can't do is let him within sight of the finish with a lead," Australian Richie Porte said, signalling Ineos may try and finish Pogacar off before the Pyrenees.

A great place to do that would be on the so-called Giant of Provence, Mont Ventoux, with its treeless lunar upper reaches. The peloton must climb it not once but twice on stage 11.

The race then sweeps down to the Pyrenees before a transfer back to Paris and the final day sprint along the cobbles of the Champs-Elysees where the champion will pull on the winner's fabled yellow jersey.