Japanese officials sealed off a beach 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 250km from Tokyo, who called police just before 9am 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 1.5 metres and is believed to be made of iron as it has a coating of rust.

Officials restricted access within a 200-metre radius around the object for most of the day, with bomb disposal crews seen inspecting the ball.

Some on social media joked that the mystery object was one of the orbs from popular anime series Dragon Ball, while others claimed it was a ‘Godzilla egg’.

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.

- Frank Chung, news.com.au