Fabio Jakobsen and Dylan Groenewegen sprinted next to each other for the victory when the space decreased and Jakobsen was forced out over the billboards and crashed.
Jakobsen is taken to hospital and placed in an artificial coma.
The International Cycling Union (UCI) has issued a statement condemning the incident as dangerous behavior and accusing Groenwegen of causing the crash and disqualifying him from the race.
"The competitor who caused the accident drove incorrectly, because he saw that someone was passing by on the right side and started driving to the right," says race director Czeslaw Lang.
Several other cyclists were involved in the crash, but according to the first reports, it should only be about minor injuries among the others.