Several short-range missiles flew between 70km and 200km, according to news agency Yonhap, citing the South Korean Joint Chiefs of Staff.
They were fired from the Hodo peninsula in the east of the country, said South Korea's Joint Chiefs of Staff. Hodo has been used in the past for launching cruise missiles and long-range artillery testing.
It was the first missile launch since 2017 as it steps up pressure against Washington after a failed nuclear summit.
The office of the Joint Chiefs of Staff said it was conducting joint analysis of today's tests with the United States.
The launch is the first since the North fired an intercontinental ballistic missile (ICBM) in November 2017, before declaring the building of its nuclear force complete and extending an olive branch to the South and the United States.
Its leader, Kim Jong Un, has vowed to no longer test nuclear weapons or ICBMs, but the North has conducted other weapons tests since then.
The missile firing, coming after the North's test of what it called a tactical weapons system, added to the pressure it has exerted on Washington in talks on ending the North's nuclear programme.
"It also seems clear that North Korea is angry over what appears to be a lack of flexibility in the Trump administration's position on relieving sanctions, sticking to a policy of 'maximum pressure'," said Harry Kazianis at the Centre for the National Interest, a think-tank.
Mr Kim has held two summit meetings with US President Donald Trump, the second in February in Vietnam, but the two failed to make progress on ending the North's nuclear programme due to disagreement on weapons dismantlement and sanctions relief.
Last month Pyongyang said it had test-fired what it described as a new "tactical guided weapon".
According to the North Korea news agency (KCNA), April's test of a new "tactical guided weapon" was overseen by Mr Kim himself. It said the test was "conducted in various modes of firing at different targets", which analysts believe means the weapon could be launched from land, sea or air.
It is unclear if that weapon was a missile, but most observers agree that it was probably a short-range weapon.
Last year, Mr Kim said he would stop nuclear testing and would no longer launch intercontinental ballistic missiles.
Nuclear activity appears to be continuing, however, and satellite images of North Korea's main nuclear site last month showed movement, suggesting the country could be reprocessing radioactive material into bomb fuel. The country claims it has developed a nuclear bomb small enough to fit on a long-range missile, as well as ballistic missiles that could potentially reach the mainland US.
- Reuters / BBC