Japan’s coast guard has launched a search mission to find an island off its northernmost coast that has unexpectedly vanished - taking Tokyo's territorial claims with it.

The strategically significant island is assumed to have disappeared under the chilly waters of the Sea of Okhotsk between the northern tip of Japan’s Hokkaido region and Russia, having been eroded by winds and snow.

Esanbe Hanakita Kojima was one of 158 uninhabited islands that the Japanese government named four years ago in a bid to clearly mark its territorial boundaries with Russia.

International laws dictate that islands can only be designated as boundary markers if they can be seen above the sea surface, raising concerns that Japan’s territorial waters may now have shrunk.

Locals in the nearest village of Sarufutsu apparently failed to notice the disappearance of the islet, which is around 0.3 miles off the coast of their island.