The U.S. -led United Nations Command, which oversees the South Korean side of the JSA, said the defector drove the jeep near the de facto border line.
The defection came during escalated tensions between the North and the South and almost a week after President Trump visited Seoul for his five-country Asia tour. In that short period of time, four North Korean soldiers shot as many as 40 rounds at him. But it's rare for a North Korean soldier to defect via the Joint Security Area, where border guards of the rival Koreas stand facing each other just meters (feet) away, and be shot by fellow North Korean soldiers.
"In the afternoon today, a North Korean soldier defected from a guard post on the North Korean side of the JSA toward our side and our military took him", the Yonhap news agency quoted an unidentified military official as saying.
According to the Joint Chiefs of Staff, the defector drove a auto into the northern side of the JSA before approaching an area just 10 meters (33 feet) from the Military Demarcation Line (MDL). He was unconscious and in critical condition on Tuesday, the surgeon in charge of the soldier's treatment, Lee Cook-jong, told reporters.
"He crossed from a North Korea post towards our [South Korean] Freedom House", the South said in a statement. The US has around 28,500 troops stationed in South Korea.
"Our military maintains full readiness while strengthening the alert in preparation for the possibility of provocations by the North Korean army", the JCS said. The JSA provides the adversaries with a neutral zone and has been the site of past dialogue.
It was not immediately known how serious the soldier's injuries were or why he chose to defect.
The 1953 armistice that ended the fighting but left the countries technically at war was signed in one of the blue buildings that straddle the Military Demarcation Line.
He was taken to hospital with gunshot wounds to his elbow and shoulder, South Korean officials said.
Two American soldiers also were killed in the DMZ by ax-wielding North Korean soldiers in a 1976 brawl over an attempt to trim a poplar tree.