North Korea fired around 500 shells in a live exercise Monday, around 100 of which landed on the South Korean side of the disputed maritime border, Seoul's Defence Ministry said.

"The North fired some 500 shots... and some 100 of them landed in waters south of the border," the Defence Ministry spokesman Kim Min-Seok told reporters.

The three-hour long North Korean drill triggered an exchange of fire as South Korea responded with volleys of shells into North Korean waters.