Tensions are on the rise again between North and South Korea, as the two nations have begun exchanging rocket and artillery fire across their border, according to the South Korean Defense Ministry.

Officials say this the first armed clash between the two countries in five years.

North Korea appears to have launched the first attack by firing a shell across the border. South Korean media reported it was likely that the North was aiming at a propaganda-blaring loudspeaker situated in a border town about about 35 miles north of Seoul in the western part of the border area.

The South then reportedly retaliated with tens of 155mm artillery rounds targeted towards the location where the shell originated, according to their defense ministry.

"Our military has stepped up monitoring and is closely watching North Korean military movements," the ministry said in a statement.

The South's Defence Ministry also said that the North has threatened "new military action" if the loudspeaker broadcasts are not stopped within 48 hours.

South Korea's presidential office announced that the National Security Council would hold an emergency session imminently.

South Korean news agency Yonhap is also reporting that the country has ordered civilians to evacuate from the western border, though the country's defense ministry told AFP that they could not immediately confirm the report.

The latest development came as US and South Korea were conducting their annual joint military exercises.

Beginning on Monday and titled the "Ulchi Freedom Guardian," the war games simulate the invasion of the South by the North, and involve around 80,000 South Korean and US troops, as well as countries including the UK, France, Australia, Canada, Colombia, Denmark, and New Zealand.

"Such large-scale joint military exercises... are little short of a declaration of a war," North Korea's Committee for the Peaceful Reunification of Korea, which oversees cross-border issues, said in response to the exercises last week, adding that they could even lead to "all out conflict."

Earlier this month South Korea promised "searing" consequences for the maiming of two of their soldiers, who officials said were victims of land mines planted on the border. This included the resumption of propaganda broadcasts across the border towards rival North Korea for the first time since 2004.

The North's National Defence Commission (NDC) denied the accusations that they had planted land mines, calling them "absurd."