The soldier was shot and injured by his own military as he crossed to the South Korean side of the Joint Security Area in the village of Panmunjom.
He was shot in the shoulder and elbow and was taken to a South Korean hospital, the Defence Ministry said.
A North Korean guard post is seen in this picture taken from an observation post inside the demilitarized zone separating the two Koreas, in Paju, South Korea, April 17, 2017.
In September, South Korea approved a plan to offer US$8 million in humanitarian assistance to North Korea to support infants and pregnant women, amid tensions sparked by North Korea's provocations.
The South Korean military has raised its alert level in anticipation of a possible North Korean provocation following the defection.
It's unclear what the soldier's conditions are or why he chose to defect to the South.
Two North Korean soldiers defected to the South in June after crossing the frontier at another location.
As part of his continuing tour of Asia, Trump met with Japanese Prime Minister Shinzo Abe and Australian Prime Minister Malcolm Turnbull Monday in Manila to discuss the situation in North Korea. The majority of defectors travel through China to defect to South Korea, according to Reuters.
Seoul says more than 30,000 North Koreans have defected to the South since the end of the Korean War in 1953.
It was not immediately known how serious the soldier's injuries were or why he made a decision to defect. In 1998, a North Korean solider fled to South Korea via Panmunjom.
North Korea likely doesn't have 200 aircraft to scramble even under the best circumstances, as it sorely lacks aviation fuel.
North Korea has this year been boosting its nuclear and missile capacity with a series of tests as it faces off with U.S. President Donald Trump who has vowed to stop it from being able to hit the mainland United States with a nuclear weapon.