Pyongyang has been steadily developing its weapons programme amid a standoff over talks aimed at dismantling its nuclear and ballistic missile arsenals in return for US sanctions relief.
The negotiations, initiated between former US President Donald Trump and North Korean leader Kim Jong Un in 2018, have stalled since 2019.
"North Korea fired two unidentified ballistic missiles from its central inland region toward the east coast, and intelligence authorities of South Korea and the United States are conducting detailed analysis for further information," South Korea's Joint Chiefs of Staff (JCS) said in a statement.
South Korea's military has raised its level of surveillance, and is maintaining a full readiness posture in close cooperation with the United States, the JCS added.
Japanese Prime Minister Yoshihide Suga called the missile launch "outrageous", and strongly condemned the action as a threat to peace and security of the region.
Japan's Coast Guard said the missiles landed outside its exclusive economic zone.
Both Suga and South Korean President Moon Jae-in would convene sessions of their national security councils to discuss the launches, according to their offices.