North Korea has officially confirmed the defection of a South Korean fisherman, saying an investigaton is underway.

The North's official Korean Central News Agency reported Thursday that Hwang Hong-ryon, 57, defected to the North by sea at around 4:30 pm Wednesday.

Meanwhile, South Korean authorities said the fisherman is believed to have accidentally crossed the maritime border on his fishing boat while heavily intoxicated.

The South Korean coast guard on Wednesday fired hundreds of shots and repeated broadcast warnings to prevent him from crossing the border but failed.

South Korea will demand Hwang's return through official channels but it remains unclear how the North will react.