British driver Dan Wheldon has died following a massive accident at the Las Vegas Indy 300.
Buckinghamshire-born Wheldon, 33, was one of 15 drivers involved in a crash at the second corner on lap 13 of the series' season-ending race.
Wheldon, who began IndyCar racing in 2002, was series champion in 2005 and won the Indy 500 in 2005 and 2011.
Lewis Hamilton, 2008 Formula 1 world champion, said: "This is a tragic loss at such a young age."
He said: "He was an extremely talented driver. As a British guy, who not only went over to the States but who twice won the Indy 500, he was an inspirational guy, and someone that every racing driver looked up to with respect and admiration.
"My heart goes out to his family and friends during this extremely difficult time," added Hamilton.
Wheldon was airlifted to the nearby University Medical Center where he was joined by his family - including his wife Susie and two young sons Sebastian and Oliver - but his death was announced to his fellow drivers in a meeting at the track.
Formula 1 driver Jenson Button wrote on Twitter: "Just woken up to the most horrific news. Dan Wheldon RIP."
He tweeted: "I have so many good memories of racing with Dan in the early 90s, a true fighter. We've lost a legend in our sport but also a great guy."
It was the first IndyCar fatality since 2006 when Paul Dana was killed during the warm-up for the season-opening Toyota Indy 300 at Homestead-Miami Speedway.
The accident at the Las Vegas track happened when a number of cars came into contact on turn two, sending several of them airborne, smashing into the outside wall and catch fence.
With cars burning and debris littering the track, the race was red-flagged.
Wheldon had started the race at the back of the field and had made up 10 places in the first 12 laps before the crash.
It was the first-ever death at the circuit in its 40-year history.
IndyCar chief executive Randy Bernard said: "Our thoughts and prayers are with his family."
Bernard added: "The IndyCar drivers and owners have decided to end the race in honour of Dan Wheldon and the drivers will take part in a five-lap salute."
When drivers returned to the track, Wheldon's 77 was the only number on the scoreboard.
The song Danny Boy was played followed by Amazing Grace as the teams' crew and mechanics stood around the track.
The Briton, who was driving for Sam Schmidt Motorsports on Sunday, had failed to secure a regular ride this season after being replaced by JR Hildebrand at the Panther Racing team.
Despite that, Wheldon put together a deal for the Indianapolis 500 with Bryan Herta Autosport, a race he won after Hildebrand crashed going into the final turn.
The debris we all had to drive through the lap later, it looked like a war scene from Terminator or somethingIndyCar driver Ryan Briscoe
He took up IndyCar chief Bernard's offer to pay $5m (£3.1m) if any non-regular series driver entered and won the season finale at Las Vegas.
There were 34 cars entered in the Las Vegas race - one more entry than was the case at the far bigger Indianapolis 500 circuit.
Earlier in the week, drivers had voiced concerns about speeds of close to 225mph being reached at the track during practice.
"I'll tell you, I've never seen anything like it," said driver Ryan Briscoe.
"The debris we all had to drive through the lap later, it looked like a war scene from Terminator or something. I mean, there were just pieces of metal and car on fire in the middle of the track... just debris everywhere."
The ending of the race resulted in Scotland's Dario Franchitti winning a third straight series crown, as a result of rival Will Power also been caught up in the accident.
Franchitti's only thoughts though were for his compatriot, and the 38-year-old was seen in his car in tears before setting off on the five-lap salute.