North Korea fired three missiles, including one thought to be an intercontinental ballistic missile (ICBM) on Wednesday, after US President Joe Biden left Asia following a trip in which he agreed to new measures to deter the nuclear-armed state.

South Korea's Joint Chiefs of Staff (JCS) said the three missiles were fired in less than an hour from the Sunan area of the North's capital, Pyongyang, where its international airport has become a hub of missile tests.

The first missile launched on Wednesday appeared to be an ICBM, while a second unidentified missile appears to have failed mid-flight, the JCS said. The third missile was a short-range ballistic missile (SRBM), it said.

In response, the United States and South Korea held combined live-fire drills, including surface-to-surface missile tests involving the US Army Tactical Missile System and the South Korea's Hyunmoo-2 SRBM, both militaries said.

"Our military's show of force was intended to highlight our resolve to firmly respond to any North Korean provocations, including an ICBM launch, and our overwhelming capability and readiness to conduct a surgical strike on the origin of the provocation," the JCS said in a statement.

North Korea has conducted a flurry of missile launches this year, from hypersonic weapons to test firing its largest ICBMs for the first time in nearly five years. It also appears to be preparing for what would be its first nuclear test since 2017.

US and South Korean officials had recently warned that North Korea appeared ready for another weapons test, possibly during Biden's visit, which was his first trip to Asia as president and included a summit with South Korean President Yoon Suk-yeol in Seoul.

"North Korea's continued provocations will only result in even stronger, faster South Korea-US deterrence, and bring deeper isolation upon itself," Yoon's government said in a separate statement.

A White House official said that Biden, who departed Japan on Tuesday evening, had been briefed on the launches and would continue to receive updates.

South Korean Foreign Minister Park Jin and US Secretary of State Antony Blinken also agreed to step up diplomatic efforts to reinforce extended deterrence and facilitate a new UN sanctions resolution in a phone call, Seoul's ministry said.

In Seoul over the weekend, Biden and Yoon 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.

There had been no response from Pyongyang to the diplomatic overtures or offers of aid, Biden said at the time. (Reuters)