It is a mystery that has baffled historians for more than half a century.

Ever since an American B-36 Bomber crashed near British Columbia during a secret training mission in 1950, the nuclear bomb on board has never been found.

Now, a commercial diver may have stumbled across the Mark IV bomb in the waters off Canada's west coast.

"I found something really weird, I think it's a UFO," Sean Smyrichinsky joked after he came ashore following the discovery near Banks Island.

It was "bigger than a king-size bed", flat on top with a rounded bottom and had a hole in the middle just "like a bagel," he told the BBC.