Stuntman Nik Wallenda will challenge himself once again on Friday by walking, unharnessed, across the Niagara Falls on a two-inch diameter cable.

He plans to cross the falls without any safety netting either. If he slips, his only hope will be to firmly grab the steel cable, or he will plummet 60m into the rapids below.

Local emergency personnel have been preparing in the event that this occurs.

Wallenda said the 550m-long crossing could take 30 to 40 minutes.

His great-grandfather Karl Wallenda died in 1978, after falling from a tightrope in Puerto Rico. But Nik Wallenda accomplished that same walk and said he has confidence in his own ability to cross the falls.

Wallenda has invested more than £1.2 million for the event, with much of the cost going to build and anchor the custom-made steel wire.