The missiles, believed to be Scud-types, were launched from the western city of Hwangju, BBC quoted the Joint Chiefs of Staff as saying in a statement.
They flew some 500 km and 600 km, 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, BBC added.
The latest launches happened between 05:45 local time (20:45 GMT on Monday) to 06:40, the military statement added.