SEOUL — North Korea has fired three ballistic missiles early Wednesday morning, South Korea's military has said.

Authorities in Seoul said the missiles were fired in the space of less than an hour from the Sunan area in Pyongyang.

It comes just a day after US President Joe Biden left the region, following a trip that saw him vowing to bolster measures to deter North Korea.

North Korea has been test-firing a flurry of ballistic missiles since the beginning of this year.

Japan confirmed at least two launches happened on Wednesday but acknowledged there may have been more.

Japan's Defence Minister Nobuo Kishi said first missile flew about 300km (186 miles) with a maximum altitude of around 550 km, while the second, reaching as high as 50 km, traveled around 750 km.

Kishi criticized the launches, saying they were "not acceptable" adding that it would "threaten the peace, stability and safety of Japan and the international community".

In a meeting convened after the missile launch, South Korea's National Security Council called the test a "grave provocation", the presidential office said.

The launches came hours after US President Joe Biden departed for the US on Tuesday evening, after a five-day trip that saw him visiting South Korea and Japan.

U.S. and South Korean officials had earlier warned that North Korea appeared ready for another weapons test, possibly during Biden's visit.

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

Biden had said the United States was "prepared for anything North Korea does."

The latest launches come as North Korea struggles to contain a suspected outbreak of Covid amongst its largely unvaccinated population of 25 million.

More than a million people have now been sickened by what Pyongyang is calling a "fever", and more than 68 people have died since late April.

On May 12, North Korea test-fired ballistic missiles the same day that Kim declared an "emergency" over the Covid outbreak.

South Korea has said it offered humanitarian aid, but Pyongyang is yet to respond. — BBC