The missiles were launched at around 7 a.m. (2200 GMT on Monday), the Joint Chiefs of Staff said in a statement.
South Korean and U.S. intelligence authorities were closely monitoring the situation, it said.
The launch comes amid a rise in tension on the Korean peninsula and follows another barrage of cruise missiles fired by Pyongyang off its east coast on Sunday.
North Korean state media KCNA reported last week that the country had tested a new strategic cruise missile.
