In a symbolic display of anger, North Korea on Tuesday blew up the northern section of unused roads that once linked it with the South, with the rivals exchanging threats days after the North claimed that its rival flew drones over its capital Pyongyang.

The roads’ choreographed demolition underlines North Korea’s growing anger against South Korea’s conservative government.

North Korean leader Kim Jong-un has vowed to sever relations with South Korea and abandon the goal of achieving peaceful Korean unification.

Observers say it’s unlikely Kim will launch a preemptive, large-scale attack on South Korea because of fear that an almost certain massive retaliation by the more superior forces of the United States and South Korea would threaten Pyongyang's survival.

In response to the explosions, South Korea’s Joint Chiefs of Staff said its military fired within southern sections of the border as it bolstered its readiness and surveillance posture.

The statement did not give details, but the move could have been an attempt to avert cross-border fire by North Korea.

It wasn't immediately known whether North Korea responded.

South Korea’s Unification Ministry, which handles affairs with North Korea, separately condemned the North’s detonations as a “highly abnormal” and “regressive” measure that violates previous inter-Korean agreements.

Video provided by South Korea’s military showed a cloud of white and grey smoke emerging from the explosion at a road near the western border town of Kaesong.

North Korean trucks and excavators could be seen clearing out debris. Another video showed smoke emerging from a coastal road near the eastern border. (AP)