South Korean troops traded fire in a standoff Sunday with a cornered conscript soldier who went on the run after shooting dead five members of his unit on the border with North Korea.

The 23-year-old army sergeant, surnamed Lim, had opened fire on fellow soldiers at a guard post on the eastern section of the heavily guarded frontier Saturday night.

The shooting spree left five dead and seven wounded -- and triggered a massive manhunt after Lee fled the scene armed with a K-2 assault rifle and a stash of ammunition.

A defence ministry spokesman said Lim, who apparently had a record of instability, had been tracked and cornered just before 2:30 pm (0530 GMT) Sunday near an elementary school around 10 kilometres (six miles) from the border.

"He shot at the pursuing troops and they returned fire," the spokesman said, adding that one officer had been wounded in the arm.

Local media reported that Lim's parents had been brought to the scene and had pleaded with their son to surrender.

As night fell, Lim was believed to be holed up in a small section of forest on a hill behind the school.

Some 500 residents of a nearby village, most of them elderly, were evacuated from their homes to another school building as a precaution.

"I've never known anything like this in my life," one 60-year-old villager told the Yonhap news agency.

"I stayed up all of last night. My children live far away and they're very worried about me," she said.

According to the military, Lim was due to be discharged in the next few months after completing his compulsory military service.

The conscript detonated a grenade immediately after finishing his six-hour guard duty at about 2:00 pm (0500 GMT) Saturday, then opened fire, Yonhap reported.

All those killed or wounded in the incident were members of the 22nd infantry division, in the eastern province of Gangwon.

Thousands of soldiers took part in the search for the fugitive, including special forces units, as army helicopters scanned the area from above.

- Shooter had trouble adapting -

Lim had difficulty adapting to the military, and past psychological evaluators had advised senior officers to pay him special attention, a defence ministry official who wished to remain anonymous told AFP.

This is not the first time the 22nd infantry has been involved in such an incident.

In 1984 a private belonging to the same division opened fire and threw a grenade at fellow soldiers in their barracks, killing 15.

The soldier, Cho Jun-Hee, then crossed the border to defect to the North, a move that Pyongyang's state media later confirmed.

The site of Saturday's shooting is just south of the Demilitarised Zone (DMZ) -- a buffer strip that runs the full length of the 250-kilometre (155-mile) frontier.

The four-kilometre-wide DMZ -- known as the world's last Cold War frontier -- features guard posts manned by the rival armies, barbed wire and roads bisecting minefields.

Because the 1950-53 Korean War ended with a ceasefire rather than a peace treaty, the two Koreas technically remain at war.

Many of the South Korean soldiers on border duty are young male recruits doing their mandatory two-year military service.

These young men make up a large part of the South's 691,000-strong troop presence, compared with 1.17 million in the North.

Most of the victims in Saturday's shooting were conscripts, aged from 19 to 23.

The defence ministry issued a "sincere apology" over the incident.

"We pray for the souls of the victims and express our deepest regret for the victims, the injured and their families," it said.

Bullying and cruelty in the barracks have long tarnished the armed forces, and been blamed for suicides and similar shooting incidents.

In July 2011 a 19-year-old marine conscript killed four colleagues in a shooting spree on Ganghwa island near the border.

In June 2005 eight soldiers were killed and two seriously wounded when a 22-year-old conscript threw a grenade and sprayed bullets over sleeping colleagues at a frontline guard post north of Seoul.

In both those cases the men were court-martialled and sentenced to death, although the penalty was not carried out.

The armed forces have in recent years taken steps to stamp out bullying, which they called part of a "distorted military culture".