A gunman in South Korea shot dead three people in a convenience store which he then torched Wednesday in an apparent revenge attack on the family of his former lover, police said.

The gunman's body was later discovered on the bank of a nearby river with a gunshot wound to the head in an apparent suicide.

Gun crime is very rare in South Korea and the incident in the southern city of Sejong, 120 kilometres (75 miles) south of Seoul, received blanket coverage on TV news stations.

The 50-year-old gunman, identified only by his surname Kang, opened fire with a shotgun in and outside the store, which was run by his former live-in partner, Sejong police chief Lee Ja-Ha told reporters.

The woman's current boyfriend, father and brother were all shot and pronounced dead at hospital.

The woman, who had not been present at the scene of the shooting, was taken into protective police custody for questioning.

"It was a pre-meditated crime caused by a combination of spurned affection and a row over how to divide property," Lee said, adding Kang and the woman had run the store together before they separated.

South Korea's tough gun control laws effectively outlaw ownership of firearms by most civilians.

Rare exceptions are allowed for hunters but they must store their rifles at local police stations.