The geologists estimate that there are about a 100bn tons of the rare elements in the mud of the Pacific Ocean floor.

At present, China produces 97% of the world's rare earth metals. Analysts say the Pacific discovery could challenge China's dominance, if recovering the minerals from the seabed proves commercially viable.

The British journal Nature Geoscience reported that a team of scientists led by Yasuhiro Kato, an associate professor of earth science at the University of Tokyo, found the minerals in sea mud at 78 locations.

The minerals were found at depths of 3,500 to 6,000 metres (11,500-20,000 ft) below the ocean surface.

One-third of the sites yielded rich contents of rare earths and the metal yttrium, Mr Kato said. Mr Kato estimated that rare earths contained in the deposits amounted to 80 to 100 billion tonnes.

The US Geological Survey has estimated that global reserves are just 110 million tonnes, found mainly in China, Russia and other former Soviet countries, and the United States.

China's apparent monopoly of rare earth production enabled it to restrain supply last year during a territorial dispute with Japan.

Japan has since sought new sources of the rare earth minerals.

The prospect of deep sea mining for precious metals - and the damage that could do to marine ecosystems - is worrying environmentalists.