Record-breaking US daredevil Nik Wallenda has made history by walking across the Grand Canyon on a tightrope, 450m above ground over the world-renowned landmark.

The 34-year-old, who walked across the Niagara Falls last year, took 22 minutes and 54 seconds while rigged up with multiple cameras and microphones broadcasting the death-defying feat live around the world.

Wallenda performed the stunt on a two-inch-thick steel cable, 1500 feet above the river on the Navajo Nation near the Grand Canyon. He wasn't wearing a harness.

The stunt means Wallenda is the first human to walk across the Grand Canyon.

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At one point during the feat, Wallenda began praying.

"That's a view there buddy. Praise God, this is awesome," he said, as he stepped out into the void. "Thank you Jesus for this beautiful view," he added.

"Praise you Jesus, how I love you," he said repeatedly, adding that there was "a lot of wind".

"Winds are way worse than I expected," he said about six minutes into the wal

He later told reporters: "I was fatigued until I was three quarters of the way across, and then it was all just adrenaline," Walenda said afterwards.

"There was dust. My mouth is extremely dry, it feels like I was walking in the desert for three weeks, not 20 minutes."

Earlier, Wallenda said he was confident in his ability.

"But the mental part is where I have to be very, very cautious. It's very challenging leading up to an event like this, it's a worldwide event ... that really plays a role on me mentally," he said.

Wallenda, a seventh generation member of the Flying Wallendas circus family, said that as he steps out he would be thinking of his great grandfather Karl Wallenda, who died in 1978 after falling from a tightrope.

Video of the fatal fall in Puerto Rico is easily viewable online, and Wallenda said it is a constant reminder of the risks - and that he must stop performing at a much younger age than his forefather, who died aged 73.

"He had said publicly that that's the way he wanted to go," the younger Wallenda said, but added: "I don't want to go that way ... I wanna die in a bed next to my wife, at an old age over 100 years old. That's my dream.

"I don't want to die performing," he added.

In last year's Niagara Falls stunt, Wallenda braved strong winds and heavy spray to walk on a cable suspended around 60m above North America's biggest waterfall, on the US-Canada border.

The Niagara walk earned him his seventh world record, after others including the highest and longest bike ride on a wire, which he performed live on NBC's Today Show in 2008.

Wallenda has been planning the Grand Canyon walk for about four years, homing in on a remote location at the eastern end of the mighty geological chasm, on land operated by the Navajo Nation Parks and Recreation.

He began final training in Florida weeks ago, boosting stamina by walking repeatedly along a 300m long rope, and using wind machines to simulate gusts of up to 80km/h.

Wallenda had admitted that a slip or mishap would boost TV ratings.

He had trained for the worst, and said that - unlike his great grand-father who had an injured collarbone and double hernia, and grabbed vainly for the wire before falling to his death - he would be able to hold on if necessary.

"It's not like I just grab with my hands like people visualise. I wrap my legs round it, my hands round it, I hug that wire like a bear hug until help comes. I've got rescue teams that would be with me within a minute," he said.

That help would be in the form of rescue trolleys, which hang underneath the cable and could be rolled out in seconds on a winch system to Wallenda, clinging on for his life.

"The networks would love it if that were to happen because it makes incredible TV," he said, adding: "But I have no desire to end up that way, that's for sure."

The walk was broadcast live in 219 countries.

- AFP with nzherald.co.nz