The missiles, believed to be Scud-types, were launched from the western city of Hwangju, the Joint Chiefs of Staff said in a statement.
They flew some 500km and 600km (311 to 373 miles), with a range enough to reach all of South Korea.
It comes after the US and the South said they would deploy an anti-missile system to counter the threats.
Tensions have soared since Pyongyang carried out its fourth nuclear test in January, followed by a series of missile launches.
