Daredevil Nik Wallenda completes his longest tightrope walk - 475 metres on a wire above a racetrack

Acrobat Nik Wallenda has completed his longest high-wire walk ever above the Milwaukee Mile racetrack during the Wisconsin State Fair, ending with a thumbs up to the crowd below giving him a wild ovation, a fair official said.

Wallenda on Tuesday took 33 minutes to walk 475 metres on a wire no wider than a U.S. nickel 10 stories above the racetrack near the state fair grounds.

Wallenda, the self-proclaimed King of the High Wire, has several records listed with the Guinness World Records organisation. His feats have included high-wire walks above the brink of Niagara Falls, between two Chicago skyscrapers while blindfolded and across the Grand Canyon, in Arizona.

Wallenda is part of the seventh generation of the famed Flying Wallenda family of acrobats. His great-grandfather, Karl Wallenda, slipped and fell to his death from a high wire in Puerto Rico in 1978.