A North Korean mine has exploded in a river in South Korea, killing one man and injuring another.

A 48-year-old man died and a 25-year-old man was seriously injured when the wooden box mine exploded as it drifted into a restricted border area in Yeoncheon, 60 kilometres north-east of Seoul.

South Korean soldiers have found more that 30 box mines an a concentrated search which began prior to this weekend's incident.

The Imjin River and all of its tributaries and inlets are being searched for the deadly North Korean weapons.

It is believed the mines have found their way into the area due to the heavy rains and water which has been released from North Korean dams.

Last year, North Korea suddenly discharged dam water, creating a flash flood and killing campers.