Rank outsider Mike Teunissen won a chaotic opening stage of the Tour de France on Saturday after a collision in the final kilometer blew the bunch sprint wide open in Brussels.

Defending champion Geraint Thomas of Ineos was caught up in that late fall, caused by Teunissen's teammate sprinter Dylan Groenewegen, but the Welshman said he was unscathed back at his team bus.

"I'm fine. I gave myself enough space and avoided the actual crash but with the barriers there was nowhere to go," Thomas said of the late spill which caught up many of the race favourites.

"The main thing is that it didn't do any damage - the bike took the hit and I just toppled over," said the unflappable 2018 champion.

The 26-year-old Jumbo-Visma suprise winner Teunissen becomes the first yellow-jersey holder on the 2019 Tour and the first Dutchman to lead the race since Erik Breukink 30 years ago.

He also becomes the 267th ever yellow jersey wearer on the centenary of the introduction of the overall leader's jersey.

"Now I have this lovely jersey and no-one can ever take it away from me," said the ecstatic winner.

"I started cycling with these kind of dreams. It's a dream come true. I'll remember this day for a long, long time."

"Eddy (Merckx) told me it was a good, clear win, I can't tell you how much that meant to me," he said after the Belgian legend helped him on with the jersey.

Fuglsang Shocked And Bloodied

Teunissen edged Peter Sagan by a few centimetres on a slightly uphill sprint in a photo finish at the winning line, the Slovak will wear the green sprint points jersey Sunday after he won the early intermediate sprint leaving him and Teunnissen on 50pts each.

Australian rookie Caleb Ewan took the young rider's white jersey after staying clear of the crash and finishing third.

"I actually got caught right behind the crash, my legs were fine so it's a shame," said the 24-year-old Ewan on his debut Tour.

The race was marked by another fall ahead of Groenewegen's, who many tipped for the stage win, which came as the tension mounted a kilometre from home.

One of the Tour de France overall favourites, Denmark's Jakob Fuglsang also crashed 18km from the finish but struggled back to the peloton looking shocked and bleeding from the head.

"He's had three stitches to the eyebrow and he needs an x-ray to check out his knee," Astana's team director Alexandre Vinokourov revealed.

"He looks okay but it's never a good thing to fall heavily like that, to win a Tour you need a bit of luck," said the former Tour rider.

Van Avermaet Bags Belgium A Jersey

Greg Van Avermaet claimed the first King of the Mountains polka dot jersey after winning an intense struggle on the 7.8 percent gradient Mur de Grammont climb at 45km, which often features in the Flanders one-day classics.

The 34-year-old Belgian Van Avermaet, on his golden Olympic champion bike, was in Saturday's early breakaway, from which he also came second on the day's other, lesser, Bosberg climb securing the polka dot jersey after just 50km.

The combativity award was won by 32-year-old Frenchman Stephane Rossetto, on his first Tour de France, after he launched a concerted solo bid from 70km out.

Half a million fans and well-wishers turned out as the race embarked in balmy sunshine from Brussels city centre, passing the Grand Place, the Royal Palace and the European Commission building before a 194.5km loop through the lush Belgian plains.

King Philippe of Belgium, national cycling hero Merckx and Prince Albert of Monaco were on hand to give the official start signal after setting off from the majestic Grand Place.

But one notable figure missing was Chris Froome, the four time Tour de France champion who is recovering from a horrific crash last month.

Sunday's stage is a technically tricky team time trial with a 27.2km Brussels city-centre route, with Deceuninck and Ineos the favourites.