About 1.5 metres in diameter, the mysterious metal sphere has been the source of intense speculation online

Police and residents in a Japanese coastal town have been left baffled by a large iron ball that has washed up on a local beach, with authorities admitting they have no idea what it is – only that it isn’t about to explode.

The sphere, measuring about 1.5 metres in diameter, has been at the centre of fevered speculation since it washed up on Enshu beach in the city of Hamamatsu on the country’s Pacific coast, local media reports said.

Fears that it could be a stray mine were dismissed after experts used X-ray technology to examine the object’s interior and found that it was hollow.

There are no indications, either, that it was involved in espionage by nearby North Korea or China.

The presence of two raised handles on the sphere’s surface – indicating it can be hooked on to something else – prompted a more prosaic explanation: that it is a mooring buoy that had simply worked loose and floated off.

Police began inspecting the ball, which is orangey-brown with what appear to be darker patches of rust, after a local woman spotted it resting on the sand just metres from the shore while she was out for a walk earlier this week, Asahi TV reported.

Officers cordoned off the area and called in explosives experts dressed in protective clothing to investigate further, but reports say authorities still don’t know what the sphere is or where it came from.

Photographs have been sent to the Japanese self-defence forces and coast guard for further examination.

One local man who regularly runs on the beach said he did not understand why the ball had suddenly become the centre of attention. “It’s been there for a month,” he told public broadcaster NHK. “I tried to push it, but it wouldn’t budge.”

At one point, police blocked off a 200-metre radius around the ball while experts tried, unsuccessfully, to solve the mystery.

There were suggestions it resembled something from the popular manga series Dragon Ball, while others believed it was a UFO that had fallen from the sky.

TV footage of the object prompted speculation on social media, coming so soon after Japan said it “strongly suspected” several Chinese spy balloons had been spotted over its territory in recent years.

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