A fleet of 11 ghost ships containing the rotting remains of sailors has washed up on the Japanese coastline, sparking an investigation in the country.

The mysterious ships have given rise to numerous conspiracy theories in the country, as authorities battle to discover the identities of the bodies.

Rescuers told Japanese broadcaster NHK that the bodies of at least 20 sailors were ‘badly decomposed’ and ‘skeleton-like’.

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Gruesome: Workers on board one of the fleet of ships that has washed up on the Japanese coastline in recent weeks, with the 'badly decomposed' of 20 sailors on board

Mysterious: Authorities are baffled as to where the mystery fleet of ships came from, with the only clues being a scrap of material that appears to be from a North Korean flag and lettering on a ship that seems to read 'Korean People's Army'

Four of the ships washed up in early November, and seven more have been spotted in recent weeks drifting in the Sea of Japan.

The most recent, discovered on Tuesday, was found off the coast of Fukui, some 250 miles north of Tokyo.

It has been impossible to identify the bodies and authorities have no idea where they might have come from.

The only clues as to where the boats may have come from are a scrap of material that appears to have come from a North Korean flag, and writing on one of the boats that seems to read ‘Korean People’s Army’.

Some believe that the vessels are fishing boats from North Korea, as the nation is trying to expand its fishing industry to boost harvests.

Clues: One of the only clues authorities have to go on is a scrap of material that seems to come from the North Korean flag

Breadcrumbs: A hand-made sign on one of the discovered ships reads the 'Korean People's Army'

Sightings: The fleet of some 11 vessels has appeared at several locations along the Japanese coast, with the most recent found off the coast of Fukui, some 250 miles north of Tokyo

But the lack of modern equipment, including GPS locating equipment, on board the ships means that several have gone missing.

Others believe the sailors may have been North Koreans trying to flee the oppressive rule of leader Kim Jong-un.

Coastguards told broadcaster NHK that the crews may have been drifting for months on end without anyone knowing where they were.

The primitive design of the vessels suggests that they were not created in the West.

It is believed that the boats have come to light now, following recent storms which may have swept them towards the coastline.

Investigation: An investigation has been launched, but conspiracy theorists believe the sailors were either fishermen, or were trying to flee the oppressive rule of Kim Jong-un