The discovery of the deposits could pit Japan against China to become the world's largest producer of the materials, The Wall Street Journal reported Wednesday.
Japan started seeking its own rare-earth metals after China held back shipments in 2010 during a dispute over islands both countries claim, Reuters reported in 2014. As a major electronics manufacturer, Japan needs rare earths for components.
Separately, China back exports of certain types of rare earths starting 2010, which caused prices to jump by as much as 10 times — further pushing Japan to seek other sources, according to the Journal.
Extracting those metals from the seabed, however, is an expensive affair, the Journal reported. A consortium of Japanese government-backed entities, companies and researchers plans to conduct a feasibility test within the next five years, according to the Journal.