Photos have emerged of a fishing boat capsized on the beach in Kanazawa in central Japan.
The skeletal bodies were discovered with a cigarette box with Korean letters on, but the authorities have not confirmed the origin of the bodies.
There was also a badge of the North Korean leader Kim Jong-un inside the wreckage.
North Korean residents must wear a badge displaying their support for the regime.
Senior police official Hiroshi Abe said: “It is difficult to identify the bodies as they had begun to decompose.
“We spotted a tobacco box which carries some Korean letters, but we can’t confirm the boat came from North Korea.”
Experts think the people on the ships were probably fishermen from North Korea in search of bigger catches and following strict government orders.
The bodies did not show any external wounds and experts think the fishermen died some time ago given the stage of decay of their bodies.
A food shortage in North Korea is leading to poorly equipped North Korean fishing boats washing up in Japanese waters.
Their vessels are often without safety features, often run out of fuel and the fishermen do not have the facilities to call for help.
Last year, 104 North Korean fishing boats washed up on Japan’s coast.
It is thought that sometimes the fishermen die at sea and then their boats are washed up onto the shores of Japan.
An autopsy of one of the men on the boat shows he was aged between 30 and 50 and died in September last year.
Japan has installed a US-built defence system amid anxiety over North Korea’s nuclear ambitions.