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 deposits have a heavy concentration of rare earths. Just one square kilometre (0.4 square mile) of deposits will be able to provide one-fifth of the current global annual consumption,” said Yasuhiro Kato, an associate professor of earth science at the University of Tokyo.
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, Mr Kato said.
The deposits are in international waters east and west of Hawaii, and east of Tahiti in French Polynesia.
Why rare earths are so important to the world’s economy
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 Malaysian government is considering whether to allow the construction of an Australian-financed project to mine rare earths, in the face of local opposition focused on the fear of radioactive waste.
The number of firms seeking licences to dig through the Pacific Ocean floor is growing rapidly.
The listed mining company Nautilus has the first licence to mine the floor of the Bismarck and Solomon oceans around Papua New Guinea.
It will be recovering what is called seafloor massive sulphide, for its copper and gold content.
The prospect of deep sea mining for precious metals – and the damage that could do to marine ecosystems – is worrying environmentalists.