A Japanese mining ship departed on Monday for a remote coral atoll to probe mud rich in rare earths, part of Tokyo's drive to curb its reliance on China for critical minerals as Beijing tightens supply.

The month-long mission of the test vessel Chikyu near Minamitori Island some 1,900km (1,200 miles) southeast of Tokyo, will mark the world's first attempt to continuously lift rare-earth seabed sludge from 6km (4 miles) deep onto a ship.

Japan, like its Western allies, has been reducing its dependence on China for the minerals vital to the production of cars, smartphones and military equipment, an effort that has taken on urgency amid a major diplomatic dispute with Beijing.

"After seven years of steady preparation, we can finally begin the confirmation tests. It's deeply moving," Shoichi Ishii, the head of the government-backed project told Reuters, as the vessel departed the port city of Shizuoka on a bright sunny day, with a snow-capped Mount Fuji in the background.

"If this project succeeds, it will be of great significance in diversifying Japan's rare earth resource procurement," he said, adding that recovering the key minerals from 6km below sea level would be a major technological achievement.

The vessel, with 130 crew and researchers, is scheduled to return to the port on February 14.

Reducing reliance on China won't be easy

Last week, China banned exports of items destined for Japan's military that have civilian and military uses, including some critical minerals. The Wall Street Journal reported Beijing has also begun restricting rare-earth exports to Japan more broadly.

Japan has condemned China's dual-use ban but declined to comment on the report of a broader ban, which China has not confirmed or denied. Chinese state media, though, have said Beijing was weighing the measure.

Finance ministers from the Group of Seven industrial powers will discuss rare-earth supplies at a meeting in Washington on Monday, sources familiar with the matter told Reuters.

Japan is no stranger to facing China's wrath over rare earths. In 2010, China held back exports following an incident near disputed islands in the East China Sea.

Since then, Japan has reduced its reliance on China to 60% from 90% by investing in overseas projects like trading house Sojitz's tie-up with Australia's Lynas Rare Earths, and promoting rare-earths recycling and manufacturing processes that rely less on the minerals.

The Minamitori Island project, however, is the first to attempt to source rare earths domestically.

"The fundamental solution is to be able to produce rare earths inside Japan," said Takahide Kiuchi, executive economist at Nomura Research Institute.

"If this new round of export controls ends up covering a lot of rare earths, Japanese companies will again make efforts to move away from China, but I don’t think it will be easy," he said.

For some heavy rare earths, such as those used for magnets in electric- and hybrid-vehicle motors, Japan is almost totally dependent on China, analysts say - a major risk for its key automotive industry.

Long-term project

Since the 2010 scare, the Japanese government and private companies have built stockpiles of the minerals, though they do not disclose volumes.

At a New Year's party for Japan's mining industry on Wednesday, several executives said they were better prepared than before to cope with the potential disruption, citing Japan's diversification efforts and stockpiles.

But Kazumi Nishikawa, principal director of economic security at the trade ministry, said the government had to continually remind companies to diversify their supply chains.

"Sometimes, you know, some event happened, then the business reacts, but the event finishes, the business forgets. We have to maintain continuous efforts," Nishikawa said on the China Talk podcast this week.

The Minamitori Island project, into which the government has sunk 40 billion yen ($250 million) since 2018, is also a long-term play.

Its estimated reserves have not been disclosed and no production target has been set. But if it succeeds, a full-scale mining trial will be conducted in February 2027.

Mining the mud was previously viewed as uneconomical due to high costs. But if supply disruption from China continues and buyers become willing to pay higher prices, the project could become viable in coming years, said Kotaro Shimizu, principal analyst at Mitsubishi UFJ Research and Consulting.

China is keeping a close watch. When the ship was conducting surveys around the island in June last year, a fleet of Chinese naval ships sailed nearby, Ishii said.

"We feel a strong sense of crisis that such intimidating actions were taken," he said. China said its actions were in line with international law and called on Japan to "refrain from hyping up threats".