The suspected ballistic missile launch was detected around 7.27am on Tuesday local time from an inland area of North Korea toward the ocean off its east coast, South Korea's Joint Chiefs of Staff (JCS) said in a statement.
South Korea's National Security Council held an emergency meeting where members expressed "strong regret" that the missile test came at a time when regional stability is extremely important, and urged North Korea to resume dialogue and cooperation, the presidential Blue House said in a statement.
The US military's Indopacific Command (INDOPACOM) said it was aware of the test and was coordinating with its allies and partners.
"While we have assessed that this event does not pose an immediate threat to US personnel or territory, or to our allies, the missile launch highlights the destabilising impact of the DPRK's illicit weapons program," INDOPACOM said in a statement, using the initials of North Korea's official name.
Japan's defence ministry said that if the projectile followed a normal trajectory for ballistic missiles it would have flown less than 700km, similar to recent tests of short-range ballistic missiles by North Korea.
"The recent actions of North Korea, such as the multiple launches of projectiles including ballistic missiles, are actions that threaten the peace and safety of Japan and the surrounding regions, and we strongly condemn it," Japan's chief cabinet secretary Hirokazu Matsuno said at a daily briefing in Tokyo.
Coming after nuclear-armed North Korea claimed to have tested a hypersonic missile on Wednesday, the launch underscored leader Kim Jong-un's New Year's vow to bolster the military at a time when talks with South Korea and the United States have stalled.
Japanese Prime Minister Fumio Kishida noted the United Nations had just finished holding discussions on how to respond to last week's launch.
"That North Korea continues to launch missiles is extremely regrettable," he told reporters.
Tuesday's apparent launch came a day after the United States mission to the United Nations, joined by France, Ireland, Japan, the United Kingdom and Albania, issued a joint statement condemning last week's test.
"These actions increase the risk of miscalculation and escalation and pose a significant threat to regional stability," US Ambassador Linda Thomas-Greenfield said in the statement on Monday.
UN Security Council resolutions ban all ballistic missile and nuclear tests by North Korea, and have imposed sanctions over the programs.
Thomas-Greenfield reiterated calls for countries around the world to enforce sanctions, and for North Korea to return to talks and abandon its missiles and nuclear weapons.
North Korea has said it is open to talk, but only if the United States and others drop "hostile policies" such as sanctions and military drills.
Last week, South Korean military officials cast doubts on the capabilities of the "hypersonic missile" North Korea claimed to have test fired on Wednesday, saying it appeared to represent limited progress over Pyongyang's existing ballistic missiles.
