New Zealand rider Jesse Sergent suffered a broken collarbone when he was knocked from his bike on the Tour of Flanders by a service car.

New Zealand cyclist Jesse Sergent will undergo surgery on a broken collarbone suffered when he was hit by a neutral service vehicle while leading the Tour of Flanders in Belgium on Sunday (NZT Monday).

Sergent, who rides for the Trek Factory Team, was leading a seven-strong break 100kms from the finish of the 265km classic when he was sideswiped by a Shimano neutral service car.

"It was evident that the trajectory of the turn was on the left side, so it's normal that the riders are moving on the left side," said Luca Guercilena, Trek Factory Racing's general manager.

New Zealand Trek rider Jesse Sergent.

"It's difficult to understand why a driver was just accelerating instead of [braking].

"It's true that something like this can happen in a race but still, it's a surprise, because these things, they should not happen."

Sergent was a key rider for the spring classics, and it was followed with a second rider also knocked off his bike when the service vehicle rear-ended a team car.

Race organisers have said they will conduct a full inquiry into what led to each of the incidents.

There were five New Zealand riders in the monument race which ends the series of Belgian classics – Sergent, Hayden Roulston, Jack Bauer, Sam Bewley and Shane Archbold, with Bauer the best finishing six minutes from Norwegian winner Alexander Kristoff (Team Katusha).

He edged Dutchman Niki Terpstra (Quick Step), with Belgium's Greg Van Avermaet (BMC) rolling in 7 seconds behind them for third place.

French rider Sebastien Chavanel was about to be assisted by his FDJ team car when the neutral service car failed to brake in time and crashed into the rear of the team vehicle, which sent the rider flying onto his back. Chavanel did not restart the race.

Kristoff outsmarted his rivals to win the race.

"It was not easy, with Niki but I'm really happy, I had great legs today," said Olympic bronze medallist Kristoff who joined the Russian team in 2012.

Briton Geraint Thomas, who was among the top favourites, did not follow the decisive move and ended up outside of the top 10.

Terpstra attacked about 25km from the finish and Kristoff jumped into his wheel before the duo built a 30-second lead over a group of favourites.

After 23km of collaboration, Terpstra, knowing that Kristoff is a much faster sprinter, refused to take turns in front but the Norwegian, winner of the Three Days of La Panne warm-up race this week, did not panic.

He waited for Terpstra to make his move in the final straight and easily outsprinted the 2014 Paris-Roubaix champion.