Egan Bernal has moved into the overall Tour de France lead after a hailstorm around 20km from the finish of stage 19 in the Alps left the road impassable.
A localised storm in Val d’Isere forced race organisers to halt the stage and a statement said times would be “frozen” at the top of the day’s previous climb.
Bernal, who started the day 90 seconds behind Julian Alaphilippe, led the Frenchman by two minutes at that point.
Ineos team-mate and defending champion Geraint Thomas remains third overall.
The result leaves 22-year-old Bernal in a strong position to win his first Grand Tour race with one more day in the mountains before Sunday’s finale with tradition dictating that the leader of the race after Saturday’s stage is not challenged in Paris.
“It’s incredible,” he said. “When I had the yellow jersey I wanted to cry.”
Initial indications were that Bernal would be awarded the stage win, but a later statement said there would be no stage winner with times taken on the top of what proved to be the day’s final climb, the Col de l’Iseran.
The official timings have Bernal 50 seconds ahead of Thomas and fellow rivals for the overall win Steven Kruijswijk and Emanuel Buchmann at that stage. Alaphilippe was two minutes, seven seconds back.
That means Bernal, who picked up an eight-second time bonus for being first up the Col de l’Iseran, will take a 45 second lead over the Frenchman into Saturday’s penultimate stage, with Thomas a further 18 seconds back.
The Welshman, who had attacked 6km from the summit of the Col de l’Iseran, reached the top around one minute clear of Alaphilippe. He had started the stage 95 seconds adrift.
Bernal, who followed Thomas’ initial attack before racing clear himself, was first to reach the 2,770m summit – the highest point in this year’s race – along with Britain’s Simon Yates.
However, as the riders raced down the mountain to Val d’Isere in preparation for what should have been the final climb of the day to Tignes, television pictures showed snowploughs trying to clear the road and race officials made the decision to halt the stage.
Video posted on social media also showed a landslide blocking the road from Val d’Isere to Tignes.
Team Ineos boss Dave Brailsford said: “First and foremost there has been a considerable landslide and you have to make sure everyone is alright. There is bike racing and then the health and safety of everyone.
“Fortune favours the brave. We said we’d take it on. We thought we could make the difference on the Col de l’Iseran and I thought the guys rode really well.
“Wout [Poels] really pushed the tempo, we had a plan, G [Geraint Thomas] went first and Egan [Bernal] went and really pushed it out over the top of the climb.
“There was a downhill and another climb to come, We don’t control the weather. I’m happy in one way but concerned in another, I hope everyone is OK.”
Disastrous day for the French
For Alaphilippe, those times could be a blessing. Although he was making up a few seconds on the descent of the Col de l’Iseran, he would likely have lost more time on what would have been a final 7.4km ascent to Tignes.
However, given the way Alaphilippe was left behind on the Col de l’Iseran, it is hard to see him coming back on Saturday’s final day in the Alps which features three more climbs, with the finale being a 33.5km ascent to Val Thorens.
“I don’t think it is possible,” said Alaphilippe when asked if he could regain the yellow jersey that he has worn for 14 days in this year’s race. “I have been beaten by something that is stronger than me, that’s how it is.
“I have no regrets. It was a dream to wear it, I carried this dream longer than I had hoped and I beat myself up every day to keep a hold of it. From the moment I took hold of the yellow jersey I dreamed but I never thought I could win the Tour.”
And hopes of a first home victory since Bernard Hinault won the last of his joint-record five titles in 1985 were earlier dented when Thibaut Pinot was forced to abandon the race.
Pinot started the day one minute, 50 seconds behind Alaphilippe but quit in tears, with his Groupama FDJ team confirming it was because of a thigh injury picked up on stage 17.