What appeared to be a wet patch of road brought down four of the team members at a tight corner.
GC contenders Primoz Roglic and Steven Kruijswijk were among those who went down in the group collision, which Eurosport commentator Carlton Kirby described as a "disaster".
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Lennard Hofstede and Neilson Powless were the other two Jumbo riders to hit the deck as a result of the incident, as confirmed by the team, who were considered favourites to claim the opening stage.
UAE Team Emirates also reportedly suffered a crash on the same corner.
Jumbo-Visma were seven seconds down at the first check just ahead of the crash.
'There was water on the road all of a sudden!' - Bennett
The team reported that the crash resulted in them losing 40 seconds on stage winners Astana.
Images from the scene showed that water had spread across the road.
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Tour de France
Pogacar holds up Roglic's number in tribute