A North Korean soldier was shot and injured by his own side on Monday while defecting to South Korea at the truce village of Panmunjom, the South's military said.
The military armistice commission of the United Nations said it had informed the North Korean military that the soldier, who was found on the south side of the border village of Panmunjom about 50 metres (150 feet) south of the Military Demarcation Line, had been undergoing surgeries for his gunshot wounds.
"He crossed from a North Korea post towards our [South Korean] Freedom House", the South said in a statement.
It wasn't immediately known how serious the soldier's injuries were or why he made a decision to defect.
"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 United States and South Korea on Saturday started joint naval exercises that will involve three USA aircraft carriers in what military officials describe as a clear warning to North Korea.
North Korea has typically accused South Korea of enticing its citizens to defect, something the South denies. An estimated 1,000 people flee Kim Jong Un's volatile regime each year, but going through the DMZ - fortified with land mines, barbed wires and machine guns - have been extremely rare because of the unsafe conditions.
From 2012 to 2016, only four North Korean troops are known to have defected to South Korea.
"His organs are extremely damaged... we do not know how long he can hold up", Lee said, describing the soldier's condition as "very serious". They stand only several yards away from tall South Korean soldiers wearing aviator sunglasses and standing motionless like statues.
The defection came at a time of heightened tension over North Korea's nuclear weapons program, and as President Trump wraps up a 12-day visit to Asia.
The fall is believed to be a result of tighter government surveillance and reinforced border security by both North Korea and China.
How many North Koreans defect annually?
The 1984 exchange of gunfire happened after North Korean soldiers crossed the border and fired, according to the U.N. Command.
There was no immediate comment on the incident from North Korea.