Huy - Tour de France organisers stopped the race just over 100km into the third stage on Monday after leader Fabian Cancellara was caught up in a massive crash.
Cancellara gingerly got back on his bike and carried on but three riders abandoned, including Australian Simon Gerrans.
After just over 10 minutes, the race was restarted behind the Tour director's car on the first categorised climb of this year's race, the fourth category Cote de Bohissau with 53km left to ride.
At the top of the hill, for which no points were awarded, the race proper recommenced.
On a straight road in clear conditions with bright sunshine, FDJ rider William Bonnet clipped the wheel of Warren Barguil in front and went down suddenly, causing a ripple through the peloton that took down scores of riders.
Amongst them was the yellow jersey wearer, Cancellara.
Such was the seriousness of the crash that organisers immediately neutralised the race for a short spell as medics and team officials tended to the injured.
Having briefly restarted the race, organisers then stopped it completely.
Bonnet was forced to abandon the race, as was Tom Dumoulin, who was third overall at six seconds and the holder of the best young rider's white jersey.
Dumoulin was even helped into an ambulance.
For Australian team Orica GreenEdge's leader Gerrans it was more Tour heartache.
Two years ago he spent two days in yellow but last year was taken out by Mark Cavendish in the sprint finish on the first stage and had to abandon there and then.
And now this time the 35-year-old made it only to the third stage.
At the time of the race stoppage, four riders from the day's breakaway - Jan Barta, Martin Elmiger, Bryan Nauleau and Serge Pauwels - were holding a lead of a handful of seconds over the peloton.