South Korea said the launches began early Wednesday morning.
South Korea’s military said North Korea fired three ballistic missiles off its east coast hours after US President Joe Biden wrapped up a visit to the area.
South Korea’s Joint Chiefs of Staff said the first missile was launched at 6 a.m. local time (21 a.m. GMT) on Wednesday, a second launch 37 minutes later and a third five minutes later.
The military said it was “maintaining a complete readiness posture” and working closely with the US.
South Korea’s newly elected President Yoon Suk-Yeol immediately convened a meeting of the National Security Council.
North Korea has carried out a number of record missile launches this year, including the largest intercontinental ballistic missile test since 2017.
The US has warned that Pyongyang is ready for more weapons tests as Biden travels to South Korea and Japan, his first visit to the region as president.
The Reuters news agency said Biden left Japan on Tuesday night but was briefed on the latest launches.
The US military command in the region said it was aware of “multiple” ballistic missile launches from North Korea and was assessing the situation.
“The missile launches highlight the destabilizing impact of the DPRK’s illegal weapons program,” it said in a statement, referring to North Korea by its official name.