The border, one of the most closely guarded in the world, is also secured by more than two million mines. The escape offer took place earlier this month, on November 2.
After being detained, the man, who was wearing civilian clothes, applied for political asylum.
The North Korean told authorities he was a former gymnast, which helped him escape.
However, there is confusion on the South Korean side as to why the defector did not trigger any of the censors along the border.
Speaking to Yonhap News Agency, an official commented, “We will look into why the sensors did not ring and make sure they are working properly.”
Thousands of North Korean dissidents, who escaped the brutal Kim Jong-un regime, are currently living in South Korea.
While a few have crossed the South Korean border, most reach the country indirectly via China.
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After being taken to hospital, it was discovered that he had parasitic worms inside his stomach, measuring up to ten inches in length.
Yeonmi Park, who entered China at the age of 13 with her mother in 2007, is one of those who managed to escape North Korea.
Describing the leak on Express.co.uk, she said: “My sister left on March 26 and four days later my mother and I followed her.
“After that, my father, my aunt, everyone was beaten and tortured because we were missing.
“But because fortunately we were following a few days later, we were not tortured.
“The rest of the family were tortured because of our escape.”
Once in China, Ms. Park fell into the hands of human traffickers.
If only after several years of servitude, she was able to escape, going first to Mongolia and then to South Korea.
Describing her ordeal, she said, “As soon as we arrived in China, the first thing I witnessed was the rape of my mother in front of me.
“They sold me my mom for at least $ 65 to $ 75 and they sold me for less than $ 300 because I was a virgin. I was 13 and a half years old.
“They sold me separately from my mother, so I was separated from everyone. We were sold to a human trafficker and so much has happened. ”