The objects were fired at 12:37 p.m. Korea time and estimated to have a flight distance of 240 kilometers (149 miles) and altitude of 35 kilometers (22 miles), South Korea's Joint Chiefs of Staff said in a statement.
The projectiles are likely part of North Korea's combined military drills, the Joint Chiefs of Staff said.
The drills began on Friday, the one-year anniversary of leader Kim Jong Un's summit in Hanoi with US President Donald Trump that ended without a deal.
North Korean state media reported that Kim presided over the exercise, which was intended to "judge the mobility and the fire power strike ability of the defense units."
Japan's Defense Ministry said it could not yet confirm if the projectiles landed inside its territory or exclusive economic zone, and said no damage had been reported to aircraft or vessels in the area.
"The recent repeated launch of ballistic missiles by North Korea is a serious problem for the international community, including Japan," it said in a statement.
South Korea Director of National Security Chung Eui-yong and other ministers are holding an urgent meeting to discuss the launch this afternoon, according to South Korea's Presidential Blue House.
The South Korean military is "monitoring related movements for possible additional launches and maintaining its readiness" said the statement from the Joint Chiefs of Staff.
If this was a missile test, it would be Pyongyang's first of 2020. Last year, North Korean leader Kim Jong Un said his country would continue to "steadily develop" nuclear weapons and the ballistic missiles to deliver them unless Washington changes course and abandons what Pyongyang calls its "hostile policy."
Weapons experts say test-firing missiles is an important part of improving their accuracy and reliability. North Korea conducted several launches in 2019 as diplomatic efforts between Pyongyang and Washington began to falter, but the country steered clear of testing intercontinental range missiles or detonating nuclear weapons underground.
However, a yet-to-be-released report from a United Nations panel found North Korea's weapons development continued last year in violation of long-standing UN Security Council sanctions.