One of the officials who asked for anonymity said the fire appeared to have begun at a farm near a North Korean billet. It wasn't immediately clear whether the farm was located inside or outside the DMZ. Authorities said the fire appeared unintentional, as the North Korean military was also trying to quench it.

By 3:45 p.m., the fire was within the proximity of the Dora Observatory in Paju, north of Seoul, a popular tourist destination.

There has been no report of injuries or damage so far, officials said, as the observatory was closed to visitors this day.

Access to the customs office leading to the South Korea-run industrial complex in the North's border town of Kaesong has been restricted since around 2:30 p.m.

More than 50 South Korean firefighters were putting out the fire, Paju city and military officials said, adding three helicopters were aiding the process under the approval of the United Nations Command.

Firefighters said they were experiencing difficulty extinguishing the fire due to strong winds and their inability to enter the northern side of the border. The two Koreas are technically at war since no peace treaty has been signed to end the 1950-53 Korean War.

It was not immediately clear what caused the fire, a South Korean military official said.

The Korean DMZ, the world's most heavily-armed border, runs the width of the Korean Peninsula roughly along the 38th parallel. It is guarded by more than 2 million troops on both sides.

Drought in the central part of the Korean Peninsula has caused several fires recently. As of Monday, the entire northern part of the Gyeonggi Province surrounding Seoul has been under a drought warning. (Yonhap)