Japan has identified multiple medium and heavy rare earth elements in deep-sea mud collected off Minamitori Island in the Pacific, marking a step forward in its effort to secure domestic supplies of critical minerals, Kyodo News reports.

The government-backed Japan Agency for Marine-Earth Science and Technology (JAMSTEC) said medium and heavy rare earths accounted for about 54% of the material extracted from mud samples. They included yttrium, gadolinium and dysprosium. Light rare earths, including neodymium, made up the remaining 46%.

JAMSTEC did not disclose the total volume of rare earth elements recovered.

The findings will underpin a full-scale mining test in the same area, scheduled to run for about a month from February 2027. The government plans to assess the commercial viability of industrial production by March 2028.

The discovery comes as Japan seeks to diversify supplies of rare earths, most of which are imported from China. Relations between Tokyo and Beijing have deteriorated following Prime Minister Sanae Takaichi's remarks on how Japan might respond to a Taiwan contingency. China has since tightened export controls on dual-use goods, including rare earths, destined for Japan.

Tokyo is pursuing domestic production of rare earths, which are essential for manufacturing electric vehicles, semiconductors and defence equipment.

The Cabinet Office project began in fiscal 2018. During January and February, JAMSTEC's research vessel Chikyu collected about 50 tonnes of mud from a depth of roughly 5,600 metres around Minamitori Island, about 1,900km southeast of Tokyo.

During the planned mining trial from February 2027, the project aims to recover about 350 tonnes of mud a day. The material will be transported to Minamitori Island for dewatering before being refined into rare earth elements on Japan's main island.

High extraction costs remain a key obstacle, as personnel and equipment must be transported to the remote island by air and other means.

The government said the presence of high-grade rare earth deposits within Japan's exclusive economic zone could reduce dependence on a single overseas supplier of critical minerals and strengthen domestic supply security. It intends to move ahead with further testing aimed at industrial-scale development.