TOKYO (AP) — Three more bodies and a dilapidated wooden boat have washed ashore in northern Japan in a seasonal influx that has sharply increased this year.

Winds and water currents push dozens of boats onto Japan's northern coasts annually, mostly rickety North Korean boats that lack the sturdiness and equipment to return home.

The Coast Guard said a Japanese fishing boat picked up a male body floating off the coast of Sakata in Yamagata prefecture Monday, and two more bodies washed up on the nearby beach an hour and half later. Officials are investigating if the bodies were from a boat that washed ashore Saturday.

Twenty-eight similar boat arrivals were detected in November, up from 4 last year.

Authorities are investigating 18 survivors from those boats who say they are North Korean.