Kiwi IndyCar driver Scott McLaughlin has walked away unharmed after he crashed through the fence in a terrifying high-speed accident.

The 32-year-old spun when he dipped a wheel on the grass as he attempted to maximise his entry into turn one in practice at the Grand Prix of Alabama.

The Team Penske driver sailed through the Turn 1 gravel runoff, launched rear-first and slammed the fence above the protective tire barrier.

Commentators suspected he was travelling at more than 200km/h during the crash.

McLaughlin laughed as he explained it in simple terms following the crash.

“I dropped the right rear, spun and I was flying backwards — then I ended up halfway through the fence,” he said.

“I’m upset for my team more than anything … the way it slipped through there (the fence) I’m really hoping it (the car) might be OK.

“I’m just really thankful for the safety and whatnot … little misjudgement just trying to open the apex, and I knew I was screwed about now (when the car left the track backwards).

“It was just hang on and see how we go. It’s not a laughing matter, it’s a mistake and I need to be better.”