US stock car racer Kurt Busch has escaped unharmed after a hard crash into the outer wall during a practice session for Sunday’s 98th Indianapolis 500.

Busch is trying to become only the fourth racer to compete on the same day in two US oval classics that total 1,770 kilometres – the Indy 500 and US stock car racing’s Coca-Cola 600 night race.

While running in a group of cars on Monday, Busch lost control coming out of turn two at the Indianapolis Motor Speedway and slammed into the outer wall, the rear of his car erupting into flames as it spun to a rest on the infield grass.

Busch climbed out of the car himself and was checked out at the track medical centre and released with approval to drive once again.

“I was starting to feel comfortable, and that’s when I made the mistake of just letting my guard down or settling into that long run-type mentality,” said Busch.

“With an Indy car you have to be on edge. You have to keep track of where you are at all times and the adjustments in the car. Maybe I just didn’t keep up with keeping the car underneath me.”

Busch is set to start on the outside of the fourth row on Sunday at Indy.

Qualifying for the stock car event at Charlotte Motor Speedway will take place on Thursday.