North Korea fired three ballistic missiles off its east coast on Wednesday, Seoul's military said, just hours after US President Joe Biden left the region following a trip in which he agreed to boost measures to deter the nuclear-armed state.

South Korea's Joint Chiefs of Staff said the three ballistic missile launches were fired in the space of less than an hour from the Sunan area of the North's capital Pyongyang. Japan's coast guard also reported at least two launches, and Japanese broadcaster NHK said the missiles appeared to have fallen outside Japan's exclusive economic zone.

The missile launches came just hours after US President Joe Biden left Japan following his first trip to Asia as president. US and South Korean officials had warned that North Korea appeared ready for a weapons test, possibly during Biden's visit.

In Seoul over the weekend, Biden and his South Korean counterpart Yoon Suk-Yeol agreed to hold bigger military drills and deploy more US strategic assets if necessary to deter North Korea's intensifying weapons tests.

But they also offered to send COVID-19 vaccines to North Korea as the isolated country battles its first confirmed outbreak, and called on Pyongyang to return to diplomacy.