A SOUTH Korean man has escaped four decades after he was kidnapped by North Korea while fishing near the disputed Yellow Sea border, officials say.

The 68-year-old, identified as Jeon Wook-Pyo, made it to Seoul recently after escaping from North Korea in early August, a government official said.

"He is now under investigation by security authorities," the official said, declining to give details.

South Korean says more than 500 of its citizens - most of them fishermen - have been abducted by North Korea in the 60 years since the end of the 1950-53 Korean War.

Those who manage to make it back to the South are often treated with initial suspicion, and subjected to a rigorous screening program to ensure they are not operating as North Korean spies.

Mr Jeon was among 25 fishermen aboard two boats that were seized by a North Korean navy ship on December 28, 1972.

The whereabouts of his fellow crewmen are currently unknown.

An activist group said earlier that Mr Jeon had stayed in an undisclosed third country - most likely China - after fleeing the North on August 11.

He then sent a letter to South Korean President Park Geun-Hye seeking assistance, saying he wanted to spend his remaining days in his hometown, the group said.

South Korea has repeatedly urged North Korea to free remaining abductees, but Pyongyang insists it is holding no one against their wishes.

Since 2000, 28 former South Korean soldiers who were listed as killed in action have been confirmed alive in the North, with 13 of them showing up for reunions with their southern relatives.

The two nations have remained technically at war since 1953 because no peace treaty was ever signed. There are no mail, telephone or email exchanges between ordinary citizens across the heavily fortified border.

Many do not even know whether relatives are alive or dead.