Cart chairman Joe Heitzler said: "What went through my mind immediately was, 'Dear Lord, dear Lord, please let this man be OK.'"

Heitzler visited Zanardi in hospital on Sunday and prayed by his bedside.

He said: "When I saw him, I couldn't believe how good he looked for what he'd been through.

The crash occurred when Zanardi lost control coming out of the pits and veered into the path of Alex Tagliani, who was driving at 200mph.

Zanardi remains in a critical condition after losing both legs in the high-speed crash, and has been put in an artificial coma by doctors in hospital, in Berlin.

"His condition can no longer be described as extremely life-threatening but remains critical," said a hospital spokeswoman.

Fellow racers Johnny Herbert, Jimmy Vasser, Dario Franchitti and team-mate Tony Kanaan gathered at the hospital on Sunday with Zanardi's wife, Daniela.

Herbert flew in from Atlanta when he heard about the crash, and Tagliani also visited after being released from hospital on Sunday with minor back injuries.

Herbert, a former Formula One team-mate of Zanardi's, said: "It's a big shock to everybody.

Mo Nunn team spokesman Laz Denes, who saw the crash from the pits, said: "I knew it could be fatal.

"All of our knees buckled. We thought, 'Oh, my God,' and we all just turned and groaned."

Earlier, Doctor Walter Schaffartzik said the 34-year-old had to have both legs amputated in an operation which lasted more than three hours on Saturday night.

Cart director of medical affairs, Steve Olvey, said Zanardi had also suffered several pelvis fractures which did not require surgery.

Morris Nunn, who owns the team Zanardi drove for, said: "We are devastated by the extent of Alex's injuries.

"But we are also so very thankful that he is on his way to surviving a tremendous impact.