A South Korean conscript soldier who killed five of his comrades in a grenade and gun attack is continuing a standoff with troops trying to capture him in a region bordering North Korea.

Speaking from Seoul, Al Jazeera's Harry Fawcett said the standoff had been continuing for nearly 19 hours "after the soldier engaged a checkpoint on Sunday afternoon".

A platoon leader was wounded in the gunfight. The soldier was now cornered in a densely forested area near a small town in the Goseong county.

A lockdown was in effect around the search zone, including guard posts along the Demilitarised Zone border, a four kms (2.5 miles) wide swathe of land serving as a buffer between the two Koreas since the end of the 1950-53 Korean war.

The soldier had thrown a grenade and opened fire late on Saturday night, killing five members of his unit and wounding seven at an outpost in the base at Goseong county, a mountainous region on the eastern coast of the peninsula.

The soldier was described by an official as an "introvert" and said there had been earlier concerns over his psychological health, but he was deemed fit to be deployed to the outpost after passing a test in November.

South Korea has launched a massive manhunt and given troops orders to "shoot to kill" if the soldier failed to surrender.

The two Koreas remain technically at war since the conflict ended in a truce not a peace treaty, and the border is regarded as potentially one of the world's most dangerous flashpoints.