A team led by Japan's marine science agency said Monday it has found rocks containing cobalt and other rare metals on the Pacific seafloor off eastern Japan, in an area covering around 950 sq. km, about half the size of Tokyo.

Rare metals are widely used in high-tech products. As Japan relies largely on imports, extracting mineral resources from its waters would help to stabilize supply of rare metals.

Using its Kaiko remotely operated research vehicle, the Japan Agency for Marine-Earth Science and Technology surveyed a seamount 350 km off the Boso Peninsula in Chiba Prefecture in April with Ibaraki University and two other universities, confirming cobalt-rich crusts covering a mountain ridge at depths ranging from 1,500 to 5,500 meters.

Based on the survey, the seamount is believed to be fully covered in such crusts. The team also collected samples from crusts as thick as 13 cm at a depth of 3,200 meters.

The team also found cobalt-rich deposits last year off Minamitori Island, Japan's easternmost territory.

Katsuhiko Suzuki, an agency researcher, hailed the latest findings as "significant" because the rocks were found at a relatively accessible location, enabling the team to more easily study how the crusts were formed and their distribution.

Cobalt-rich crusts contain not only cobalt, but also nickel, platinum and other minerals.