South Korea's joint chiefs of staff said it detected the launch of a ballistic missile, and the office of Japan's Prime Minister Fumio Kishida also said it was a suspected ballistic missile.
US Indo-Pacific Command said it condemns North Korea's ballistic missile launch, calling on the reclusive regime to refrain from further destabilising acts.
The launch was the ninth this year. The most recent 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.
In South Korea, where citizens are already casting votes ahead of Wednesday's presidential election, the National Security Council condemned the North'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.
Japan's Defence 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 550km and flew a distance of 300km, similar to the South Korean military's estimated 560km height and 270km 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 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.
"The timing of North Korea's missile testing may seem odd to us, given the global focus on Ukraine," Jean Lee, a fellow at the Washington-based Wilson Center, said on Twitter.
"But it makes perfect sense in North Korea, where scientists are focused on perfect new weapons for Kim to show off at a big military parade in mid-April."
North Korea's ballistic missile launches are banned by United Nations Security Council resolutions, which have imposed sanctions on the country over its weapons programs.
"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," Leif-Eric Easley, a professor at Ewha University in Seoul, said.
The United States has said it is open to talks without preconditions, but Pyongyang says talks are only possible after Washington and its allies drop hostile policies.
