As far as China is concerned, they are mere chunks of uninhabitable rock. But for Japan, these tiny specks in the Pacific, collectively known as “distant bird island”, serve as a key economic and strategic outpost at a time of growing concern over Chinese military activity in the region.

Japan announced this week it would spend 13bn yen (£75m) to rebuild an observation post on the remote island of Okinotorishima, located about 1,000 miles south of Tokyo – a move that could reignite a long-running dispute over maritime territory between Tokyo and Beijing.

In recent years, Okinotorishima has been largely overlooked while the north-east Asian rivals clashed diplomatically over sovereignty of the Senkaku islands in the East China Sea.

While China has never laid claim to Okinotorishima, Japan’s decision to devote such large sums to the atoll’s upkeep will not be welcomed in Beijing. The area contains rich fishing grounds, potentially huge deposits of oil and other energy resources, as well as rare metals.

Located roughly midway between Taiwan and the US territory of Guam, the atoll – which measures just 4.5km east to west and 1.7km north to south – is also of rising strategic importance amid tensions over China’s claims to the Senkakus and its island-building project in the South China Sea.

Chinese vessels are thought to have mapped the surrounding seabed in anticipation of submarine operations against incoming US ships in the event of a conflict, most likely over Taiwan.

Beijing has long insisted that Okinotorishima comprises rocks – not islands – that are unable to sustain human life and should not, therefore, be used by Japan to expand its exclusive economic zone (EEZ), which extends for 200 nautical miles around the atoll.

The United Nations convention on the law of the sea defines an island as “a naturally formed area of land, surrounded by water, which is above water at high tide”. The convention states that “rocks which cannot sustain human habitation or economic life of their own shall have no exclusive economic zone”.

That is why Japan has not followed China’s example in the South China Sea and created manmade islands with thousands of tonnes of sand and concrete; instead, it has tried to prevent existing coral beds from disappearing beneath the ocean, taking its EEZ with them.

Since the late 1980s, it has spent roughly $600m (£415m) building steel breakwaters and concrete casings to prevent erosion of two islets that protrude from the water at low tide; a third visible islet is covered by a titanium net to protect it from debris created by the waves.

It also constructed a three-storey observatory that monitors ships in the area and sends data to land ministry.

A ministry official told the Asahi Shimbun newspaper that the observatory needed urgent repair work before it collapsed due to erosion and regular poundings from typhoons.

“Rebuilding the facility is a necessary step to help preserve the site,” the unnamed official said. “We hope to start working on the construction as soon as possible.”