An informed source told Reuters a helicopter was taking the 41-year-old to hospital in Treviso after she was strapped into a medical stretcher and winched off the sunlit Olimpia delle Tofane piste.
Vonn, whose battle to reach the start line despite her knee injury dominated the opening days of the Milano Cortina Olympics, saw her unlikely quest halted in screaming agony on the snow.
Wearing bib number 13 and with a brace on the left knee she injured in a crash at Crans Montana on January 30, Vonn looked pumped up at the start gate.
She tapped her ski poles before setting off in typically aggressive fashion down one of her favourite pistes on a mountain that has rewarded her in the past.
The 2010 gold medallist, the second most successful female World Cup skier of all time with 84 wins, appeared to clip the fourth gate with her shoulder, losing control and being launched into the air.
She then barrelled off the course at high speed before coming to rest in a crumpled heap.
Vonn could be heard screaming on television coverage as fans and teammates gasped in horror before a shocked hush fell on the packed finish area.
She was quickly surrounded by several medics and officials before a yellow 'Falco 2' Alpine rescue helicopter arrived and winched her away on an orange stretcher.
The helicopter took Vonn initially to Cortina's Codivilla Putti Hospital for a medical assessment. As it flew overhead towards the town, spectators applauded.
"The medical team responded immediately and the intervention time was excellent," the International Olympic Committee said.
There was no immediate word on her condition.
Skiiers left shocked
Fellow American Breezy Johnson, the world champion who had set the fastest time, covered her eyes and looked away as the helicopter was called.
Johnson was later crowned champion on a bittersweet day of pride and pain for the team.
"My heart goes out to her," said Johnson, the first American medallist of the Games, who added Vonn's coach had told her she was cheering her from the helicopter.
"When you love the course so much and it hurts you like that it hurts even more."
Vonn had been hoping to become the oldest Alpine skiing Olympic medallist after winning two World Cup downhills this year and finishing on the podium in the other three.
Arguably the highest-profile athlete at the Games, the crash sent shockwaves across day two.
Her teammate, downhill skier Bryce Bennett, watching in the town square on a big screen in Bormio, where the men's races are staged, was left stunned by what he had seen.
"It's obviously a bummer. It's just like the risk of downhill is high and ... Like, everyone makes it look so easy when it's going smooth and then you see how quickly it can go in the other direction," he told Reuters.
"Her right leg didn't look so good, but we'll see."
Vonn risked too much
Even TV commentators were visibly shaken by Vonn's crash.
Double Olympic gold medallist Tina Maze, working for Eurosport, said Vonn had risked too much in her run.
"Of course if you're not healthy then the consequences are even worse, but we know all Lindsey," she said. "It's her decision that she wanted to do this no matter what.
"It's really tough for everyone here to see this and especially for her family and her teammates and everyone working with her. I mean it's terrible."
FIS president Johan Eliasch said it was a tough but tragic side of ski racing.
"I can only say thank you for what she has done for our sport because this race has been the talk of the Games and it's put our sport in the best possible light," he added. "I hope she will have a speedy recovery, and is back on skis very, very soon."
Vonn's sister, Karin Kildow, said she had put her 'whole heart' into racing at the Olympics, especially as it was being staged on a course she loves so much.
"That's definitely the last thing we wanted to see," she told NBC. "When that happens, you're just immediately hoping she's okay, and it was scary.
"She dared greatly, and she put it all out there."