Mysterious giant beasts may lurk in the darkest depths of the ocean, making whale-like noises that are baffling scientists, it was disclosed today.

Researchers have nicknamed the strange unidentified sound picked up by undersea microphones ``Bloop''.

While it bears the varying frequency hallmark of marine animals, it is far more powerful than the calls made by any creature known on Earth.

In 1997, Bloop was detected by sensors up to 4,800 km apart, New Scientist magazine reported.