A fishing boat that washed ashore in Akita Prefecture late Thursday with eight North Korean men has disappeared at the port where it was moored, police said Saturday.
On Friday, the men were taken into custody at a police station in Yurihonjo after residents discovered them standing near the seaside.
It was not immediately clear what happened to the 2-meter wooden vessel, and police said bad weather prevented them from thoroughly investigating. Police said the vessel may have sunk at the port or drifted beyond the breakwater and into the Sea of Japan.
The North Korean men told local authorities that they were fishing before their engine failed. They are not expected to seek asylum.
Chief Cabinet Secretary Yoshihide Suga said at a news conference on Friday that the government will "respond appropriately." Japan has no diplomatic relations with North Korea.
The men told investigators that they left a port in North Korea about a month ago for squid fishing and were scheduled to return in a few weeks but were cast adrift after the engine failed.
The incident comes amid escalating tensions on the Korean Peninsula as well as growing concerns in Japan about a potential refugee crisis should fighting break out with the isolated country.
North Korean fishing boats show up fairly frequently in Japan but do not always spark alarm. According to the Japan Coast Guard, 43 wooden boats have been discovered in Japanese waters this year alone, including a number of badly damaged vessels. Many are believed to be from the Korean Peninsula.