North and South Korea OPEN FIRE as they blast warning shots and artillery rockets after sea clash in dramatic escalation

NORTH and South Korea have opened fire with warning shots and artillery rockets amid boiling tensions between the two states.

An earlier clash between the two at their disputed maritime border caused North Korea to fire ten artillery rockets off its west coast early on Monday.

South Korean military had fired warning shots at a North Korean boat that crossed the two Koreas' maritime border at 3.50 am, North Korea's official KCNA said. 

In response, North Korea fired ten shells from multiple rocket launchers at around 5:15 am a spokesman for the General Staff of the North Korean People's Army said.

The South's Joint Chiefs of Staff said it sent back a North Korean merchant vessel that crossed the Northern Limit Line (NLL), the de facto sea boundary between the two Koreas.

"The General Staff of the Korean People's Army ... ordered to fire ten shots from multiple rocket launchers to sternly send back the enemy's vessel," the North Korean spokesman said in a statement carried by the KCNA.

The incident comes amid rising tensions over North Korea's recent barrage of missile tests.

Last week South Korea scrambled fighter jets after North Korean warplanes flew close to the border and Kim Jong-un fired a ballistic missile.

South Korea's military said Kim also fired a ballistic missile into the sea off its east coast from the Sunan area near Pyongyang.

And previously Kim Jong-un flew 12 warplanes close to the border, believed to have carried out air-to-surface firing drills, according to South Korea's military.

Kim fired another two ballistic missiles in a "clear warning to enemies" while earlier this month he fired a further two short-range ballistic missiles toward Japan.

South Korea says that the North is on the brink of its first nuclear bomb test in five years, with officials saying "everyone is in standby mode".