The stash of rare metals sits in a 965-square-mile patch in the Pacific Ocean near Minamitorishima Island in Japanese waters, about 1,150 miles southeast of Tokyo.
The rare-earth metals are used to make products such as batteries, mobile phones and electric cars.
China owns most of the rare-earth metals but the discovery could have a huge impact on manufacturers across the globe.
On the other hand, Japan is resource-poor and relies heavily on the manufacturing abilities of its Asian neighbours.
The report, published in Scientific Reports, says that the patch contains 16 million tons of rare-Earth oxides – equivalent to 780 years' worth of yttrium supply, 620 years of europium, 420 years of terbium and 730 years of dysprosium.
It added that the discovery "has the potential to supply these metals on a semi-infinite basis to the world”.