The latest incident follows several recent high-profile defections
A North Korean soldier has defected to South Korea by walking through the heavily mined military border zone.
The soldier was unarmed and is being questioned over how and why he made the crossing, the South's military said.
Around 1,000 North Koreans defect to the South every year through China, but the soldier took the unusual step of traversing directly across the fortified eastern border.
The Demilitarized Zone (DMZ) is a strip of land more than 250km long and around 4km wide running across the Korean Peninsula.
It was established at the end of the Korean War and acts as a buffer zone between the two countries.
Despite its name, it is heavily mined, lined with barbed wire and has soldiers on both sides.
Military officials said the soldier arrived unharmed and without any exchange of fire.
The defection comes amid heightened tensions in the region since the North conducted its fourth nuclear test at the beginning of the year and followed it with an unprecedented string of missile tests.
This month it carried out its fifth and largest nuclear test in what is seen as an attempt to counter alleged hostility from the United States.
North Korea has been in a nominal state of war with South Korea since their 1950-53 conflict ended in a truce, not a peace treaty, and there have been several high-profile defections recently that have embarrassed the North.
The most prominent defector was Thae Yong Ho, the North's deputy ambassador to the UK, who became the highest-ranking diplomat to defect to the South when he arrived last month.
In April, 12 North Korean waitresses in a restaurant in China fled to the South along with their manager, and a North Korean teenager taking part in a Hong Kong maths contest in July sought asylum at the South Korean consulate.
In 2014 another North Korean soldier successfully fled after a failed escape attempt over which he was beaten for 15 days.