South Korea has fired dozens of shells across the border into North Korea in retaliation for an apparent rocket attack, Seoul's defence ministry said.
A spokesman said South Korea had detected the trajectory of a rocket fired from the North Korea side along a western section of the border shortly before 4pm (local time).
"Our military in response launched dozens of rounds of 155mm shells towards the site from which the North Korean military launched the rocket artillery," the ministry said in a statement.
"We have strengthened our military readiness and are closely watching movements of the North's military," the statement said.
It was not immediately clear what, if any, South Korean unit had been targeted by the North Korean rocket, and there were no reports of any strike on the South side of the border.
A local government official in Yeoncheon county – some 60 kilometres north of Seoul – told AFP that residents of several border villages had been ordered to evacuate their homes for nearby shelters.