Mud samples taken from the seabed around Minamitorishima island, some 2,000 kilometres southeast of Tokyo indicated presence of massive amounts of rare earth minerals, Kyodo news agency reported.
"An estimated 6.8 million tonnes of rare earth minerals, including dysprosium, exist in the mud in the deposit, which is within Japan's exclusive economic zone," said the group headed by University of Tokyo professor Yasuhiro Kato, an expert in earth resources, yesterday.
The amount is equivalent to some 230 years' worth of domestic consumption of the minerals, which are indispensable for producing high-tech products such as hybrid cars and mobile phones, it reported.
The discovery is the first of such magnitude in Japan's exclusive economic zone.
Once a mining technique is developed to secure the minerals from the seabed, which is at a depth of 5,600 meters, Japan may be able to attain complete self-sufficiency in supplies of the mineral.
Japan now relies largely on imports from China which accounts for more than 90 per cent of rare earth elements produced in the world.
Since 2010, China has reduced its export quotas for rare earth minerals, arguing the restraints are justified to protect its natural resources and environment.
Japan, together with the United States and the European Union, on Wednesday had requested the World Trade Organisation to establish a panel to determine whether China's export restrictions on rare earth minerals are permissible under WTO trade rules, it said.