The border and its fortifications have been in place since the Korean War ended in an armistice in 1953.
The DMZ is fortified with landmines and barbed wire and guarded by tens of thousands of troops on both side. Defections across it are very rare.
In June last year, a teenage recruit from the North surrendered to his Southern counterparts at Hwacheon.
A North Korean soldier has defected to South Korea by walking across the heavily protected Demilitarized Zone (DMZ), say officials in Seoul.
The man crossed the eastern section of the border unarmed on Thursday morning, said South Korea’s Joint Chiefs of Staff (JCS), with no shots fired.
In 2012 a soldier from the North made it through rows of surveillance cameras and electric fencing before eventually managing to hand himself over – an embarrassment that cost three South Korean field commanders their posts.