A South Korean army officer gunned down five fellow soldiers on Saturday night and wounded five more members of his army unit based at a general outpost along the North Korean border.
The unidentified sergeant remains armed and is still at large, prompting the South Korean military to launch an operation to track him down, officials told the Korean Herald.
The shooting rampage began at around 8:15 PM local time in the eastern town of Goseong in Gangwon Province, according to the South Korean military.
The wounded were immediately taken to hospital, and their condition is unknown.
A motive has not yet been determined, but South Korean army officials say the incident is not linked to North Korea, but have not elaborated on those statements or the details of the shooting.
The incident comes amid elevated tensions between the opposing Koreas over the North Korea's recent rocket and missile launches and threats to "wipe out" South Korean President Park Geun-hye's government after a Seoul official said the North "must disappear soon."
There have been previous instances of violent soldier rampages on the world's most heavily armed border between North and South Korea.
Most recently, a 19-year-old marine corporal, who was thought to been mentally ill, went on a shooting spree on an Island base just south of the maritime border with North Korea.
Earlier in 2005, an army private set off a hand grenade and opened fire on fellow soldiers at a post on the frontlines of the border, killing eight and sounding several more.