An offshore powerboat racer is in critical condition at a Florida hospital following an accident at the Key West World Championship, where two racers were killed in a boating crash on Wednesday.

Super Boat International officials said on Friday night that racer Joey Gratton of University Park, Florida, was being airlifted to Ryder Trauma Centre in Miami.

His racing partner Stephen Page, the owner and driver of Page Motorsports, was admitted to Lower Keys Medical Centre. Officials say he is in good condition.

The 38-foot(11.5-metre) Superboat 850-class Skater catamaran rolled over twice in Turn 1 of the 6.5-mile(10.4-kilometre) course Friday.

The accident followed a crash on the first day of racing that killed the throttleman and driver for Big Thunder Marine.