"NASCAR has lost its greatest driver," said NASCAR Chairman of the Board Bill France, who himself is recovering from life threatening illnesses, "and I personally have lost a great friend."

Earnhardt's wife Teresa was at his side at the time of death. Dr. Steve Bohannon, emergency trauma surgeon who was on one of the ambulances that responded, said: "My speculation would be head injuries, basically to the base of the skull".

Earnhardt, who won the 1998 Daytona 500, was unconscious when he was cut from his Chevrolet after the accident between Turns 3 and 4 of the Daytona track as a tangled pack of cars raced to the checkered flag.

He was immediately transported to Halifax, less than one mile from the speedway.

Earnhardt was pronounced dead while his driver, Michael Waltrip, was being interviewed in the Daytona press box after his first career victory in 463 starts.

Dale Earnhardt Jnr finished second, and witnessed the crash. In the accident, Ken Schrader's Pontiac was pinned against the outside wall by Earnhardt's out-of-control Chevrolet, which came from a lower lane on the 31-degree banked turn.

Stewart was listed as "alert and conscious" when transported. A CT scan of his head and neck and an x-ray of his left shoulder were negative, a speedway statement revealed an hour before his death.

He suffered a concussion in the accident, in which his car flipped several times and was ultimately struck - on the bottom while flipping - by his team-mate Bobby Labonte.

Dale Earnhardt's death comes a month after a helicopter tragedy claimed the life of top Irish rally driver Bertie Fisher, and soon after a raceday crash that claimed the life of top motorcyclist Joey Dunlop.