Above: South Korean soldiers patrol the border following mine explosions
South Korea said it detected a suspected North Korean projectile heading towards the loudspeaker at around 3:52pm (6:52am GMT).
The projectile did not appear to have damaged the loudspeaker or caused and casualties, South Korea said. It landed in an area 35 miles north of Seoul and resident in the area were ordered to evacuate.
In response the South Korean military fired tens of artillery rounds towards North Korea. South Korea’s defence ministry said there had been no immediate response from the North.
South Korea’s presidential office said it was convening an urgent meeting of the national security council, it was reported.
Tensions have been rising on the peninsula since earlier this month when landmine explosions in the demilitarised zone wounded two South Korean soldiers. Seoul accused North Korea of laying the mines, which Pyongyang has denied.
Seoul then began blasting anti-North Korean propaganda from loudspeakers on the border, resuming a tactic that both sides had halted in 2004.
North Korea on Saturday demanded that the South halt the broadcasts or face military action, and on Monday began conducting its own broadcasts.
Thursday’s exchange of fire came amid ongoing annual joint US and South Korean military exercises, which began on Monday, and which North Korea regards as preparation for war.