A man survived a plunge over Niagara Falls on Wednesday and was in hospital with hypothermia and a head injury after a dramatic river rescue.

A tourist called police at about 2:15 p.m. to say he saw a man climb over the retaining wall above the Canadian Horseshoe Falls, said Sgt. Chris Gallagher of Niagara Parks police.

"The male was observed going down to the water's edge and jumping in of his own accord into the river above the falls," Gallagher said.

The man was swept over the falls and plunged almost 60 metres into the Niagara River below. Police spotted him floating about 300 metres from the base of the falls in front of a power plant, Gallagher said.

Officers yelled at him to swim to shore, but he wouldn't comply. A helicopter from a private firm was sent to retrieve the man but was unsuccessful. However, the chopper hovered above the man, using the force from its rotor blades to create a current that pushed him toward shore, Gallagher said.

Police would not identify the man, but said he appeared to be between 35 and 40 years old.

Once the man was close to shore, the fire department's river rescue unit pulled him out.

"He was suffering from severe hypothermia at the time and there was a large head wound to the top of his forehead," Gallagher said.

Police did not have any further information on the man's condition but said he was taken to hospital.

Although the man was rescued naked from the river, witness reports indicate he was fully clothed when he climbed over the wall, Gallagher said, adding it's not unusual for clothing to be ripped off by strong currents.

Niagara Parks police Chief Douglas Kane said the man "refused any assistance" from rescuers and "swam further into the centre of the Niagara River."

The man was "very fortunate to have survived, after going over the falls and remaining in the icy river for approximately 45 minutes," Kane said in a release.

The last person known to survive a trip over the falls was a Michigan man in October 2003.

Bystanders at the brink of the Horseshoe Falls said Kirk Jones climbed over a wrought-iron barricade, slid down the embankment to the rocks below, stepped into the water and went over the falls.

Other witnesses said he then apparently swam to shore.

He didn't suffer any serious injuries.