The launch was Pyongyang’s ninth round of weapons tests in 2022 as it continues to use a pause in diplomacy to expand its military capabilities.
North Korea has fired a ballistic missile toward the sea to the east of the Korean peninsula, an apparent test just days before the South's presidential election.
South Korea's Joint Chiefs of Staff said it detected the launch of one ballistic missile on Saturday and the office of Japan's Prime Minister Fumio Kishida also said it was a suspected ballistic missile.
The launch was the ninth this year. The last was on February 27 when North Korea said it tested systems for a reconnaissance satellite.
The South Korean military said Saturday's launch came from a location near Sunan, where Pyongyang's international airport is located. The region has been the site of previous tests, including the February 27 launch.
South Korea's National Security Council (NSC) condemned North Korea's "unprecedented repeated firing of ballistic missiles", which goes against peace and stability on the Korean Peninsula and the international community, according to a statement from the presidential Blue House.
South Korea will "even more closely monitor North Korea's nuclear and missile-related facilities, such as Yongbyon and Punggye-ri", and take necessary measures, the NSC said.
Pyongyang prepares for a satellite launch
Japan's Defense Minister Nobuo Kishi said the launch was "not acceptable".
"The significant pace at which North Korea is developing its missile-launching technology is not something our country and the surrounding regions can overlook," he said.
Kishi said the North Korean projectile reached a height of 550 km (340 miles) and flew a distance of 300 km (190 miles), similar to South Korean military's estimated 560 km height and 270 km range.
The launch underscores the challenges facing whoever wins Wednesday's presidential election in South Korea.
With denuclearisation talks stalled, North Korea conducted a record number of missile launches in January. It appears to be preparing to launch a spy satellite in the near future and has suggested it could resume testing of nuclear weapons or its longest range intercontinental ballistic missiles (ICBMs) for the first time since 2017.
Analysts say North Korea could use the upcoming presidential transition in South Korea or a big national holiday on April 15 to test fire a major new missile or other weapon.
"North Korea may be preparing a ‘satellite launch’ around the Kim Il-sung birth anniversary on April 15 and before South Korea conducts another satellite test of its own," said Leif-Eric Easley, a professor at Ewha University in Seoul.