The projectiles were fired at 6.53 a.m. and 7.12 a.m. from areas in the city of Kaechon, South Pyongan province, about 80 km north of the capital, Pyongyang, in an easterly direction, Yonhap News Agency quoted the Joint Chiefs of Staff (JCS) as saying.
Both flew around 330 km, the JCS said, adding that South Korean and the US intelligence authorities are analyzing their exact type. It did not provide information on their top speed.
"Our military is monitoring the situation in the case of additional launches and maintaining a readiness posture," the JCS said, calling on the North "to instantly stop such acts that heighten tensions".
In response to the latest launches, South Korea held an emergency National Security Council (NSC) meeting, presided over by Chung Eui-yong, chief of the presidential national security office, and discussed the issue.
In Washington, a senior US government official said it was aware of the latest missile launches and is closely monitoring the situation in cooperation with its allies.
The firings came just hours after the North's First Vice Foreign Minister Choe Son-hui expressed willingness to resume denuclearization talks with the US later this month and demanded Washington to come up with a new proposal acceptable to Pyongyang, Yonhap reported.
Tuesday's firings were the 10th such launches so far this year, during which the North tested new types of missiles or multiple rocket launchers in protest of joint military exercises between the US and the South.
The North last conducted such launches on August 24 and said it tested a "new super-large" multiple rocket launch system.
( With inputs from IANS )