The Joint Chiefs of Staff (JCS) said it carried out a search operation after detecting the person around 9.20pm on Saturday on the eastern side of the Demilitarised Zone (DMZ) separating the two Koreas.

“We’ve confirmed that the person crossed the Military Demarcation Line border about 10.40pm and defected to the North,” the JCS said.

The JCS said it could not confirm whether the person was alive, but sent a notice to the North via a military hotline asking for protection.

The border crossing, which is illegal in South Korea, came as North Korea carries out strict anti-coronavirus measures since shutting borders in early 2020, though it has not confirmed any infections.

A public and political uproar emerged after North Korean troops shot dead a South Korean fisheries official who went missing at sea in September 2020, for which Pyongyang blamed anti-virus rules and apologised.

Two months earlier, North Korean leader Kim Jong-un declared a national emergency and sealed off a border town after a North Korean defector who he said had Covid-19 symptoms illegally crossed the border into the North from the South.

The North’s prolonged lockdowns and restrictions on inter-provincial movement have also pushed the number of North Korean defectors arriving in the South to an all-time low.

Cross-border relations soured after denuclearisation negotiations between Pyongyang and Washington stalled since a failed summit in 2019.

South Korea and a US-led UN force are technically still at war with North Korea since the 1950-1953 Korean War ended in an armistice rather than a peace treaty.