AP

A man has plunged at least 54 metres over Niagara Falls and survived - only the third person known to have gone over without a safety device and live.

Niagara Parks Police say witnesses reported seeing the man climb over a railing at 10.20am (local time) on Monday and "deliberately jump" into the Niagara River up to nine metres above the Horseshoe Falls.

He surfaced in the lower Niagara River basin near the Journey Behind the Falls observation platform.

Horseshoe Falls, on the Canadian side of the river, is the tallest of the three main falls, higher than the American Falls and Bridal Veil Falls.

The man, believed to be in his early 40s, was rescued about two hours after he collapsed in waist-deep water near the rocky shore.

A waiting helicopter flew him to a hospital for treatment of what police said were life-threatening injuries. Police did not identify him.

Since 1901, when Annie Edison Taylor was the first person known to go over the falls and live, 17 others have replicated the feat, most by using safety devices like Taylor's oak barrel or the foam-lined pickle barrel and inner tube contraption Steve Trotter used to go over in 1985.

The last person to go over the falls unaided and survive was a 30-year-old Canadian man in March 2009.

In October 2003, Kirk Jones, an out-of-work auto parts salesman survived his plunge over the falls and in 1960 seven-year-old Roger Woodward was swept over the falls wearing a life jacket and survived.