Japanese officials sealed off a beach on Tuesday morning to investigate a large, mysterious metal sphere of unknown origin.

The “suspicious” ball was reported by a local resident in Hamamatsu, a southern coastal city about 155 miles from Tokyo, who called police just before 9 a.m. saying “a large round object was washed up on the beach”, Asahi News reported.

The woman said her husband first noticed the object while taking a walk on the weekend.

According to police, the object is a sphere with a diameter of around 4 feet, and is believed to be made of iron as it has a coating of rust.

Officials restricted access within 655 feet around the object for most of the day, with bomb disposal crews seen inspecting the ball.

An X-ray later determined the object was hollow and there was no danger of explosion, with the restrictions lifted at around 4pm, according to Fuji News Network.

The object, which has a protrusion that would allow it to be hooked onto something, closely resembles a mooring buoy, Vice News noted.

But the strange sighting sparked a brief flurry of TV attention and frenzied social media speculation, coming in the wake of the US shooting down a Chinese spy balloon followed by multiple unidentified objects.

Japanese police say they will ask local officials responsible for coastal management to collect the ball.