North Korea launches ballistic missiles, prompting 'stern protest'

North Korea has fired two short-range ballistic missiles into the sea off its eastern coast, with one flying more than 600 kilometres, according to South Korea's military.

The launches came days after Pyongyang reasserted its status as a nuclear-armed state and rejected a United Nations resolution demanding it halt its nuclear activities.

South Korea's military said the first missile was launched about 3pm on Sunday, local time, from the Wonsan area and flew about 450 kilometres into the East Sea, a body of water also called the Sea of Japan.

"Our military detected an additional short-range ballistic missile launched from the Wonsan area of North Korea towards the East Sea at around 5:50pm," South Korea's Joint Chiefs of Staff (JCS) said.

The second missile "flew more than 600 kilometres, and South Korean and US authorities are conducting a detailed analysis to determine its exact specifications", it said.

The JCS said South Korea, the United States and Japan had been "tracking and sharing relevant developments from the initial stage of the launch".

Japan lodged a "stern protest" with North Korea over the launches, condemning them as a threat to regional peace and security, the Kyodo news agency reported.

South Korea's presidential National Security Office convened an emergency security meeting following the first launch and assessed its impact on national security, the presidential office said.

The government called on Pyongyang to "immediately cease" its ballistic missile launches, describing Sunday's firings as a "grave act" that violated UN Security Council resolutions.

Weapons 'hitting the targets'

The launches came eight days after North Korea fired multiple short-range ballistic missiles towards the East Sea as part of what it later described as a joint firepower drill.

That exercise involved long-range artillery and missiles, with the weapons "hitting the targets with 100 per cent accuracy", state media reported.

North Korea accused "hostile forces" of seeking to end the country's nuclear program during this week's General Conference of the International Atomic Energy Agency (IAEA).

A foreign ministry spokesperson said the IAEA resolution "has no effect on the DPRK's position as a nuclear weapons state", using the acronym for North Korea's official name.

The North's status as a nuclear power was "guaranteed by the actual nuclear deterrent and irreversibly and permanently fixed by the supreme law of the state", the spokesperson said.

North Korean leader Kim Jong Un's sister Kim Yo Jong recently said the country's nuclear-armed status was "absolute" and called those hoping for its denuclearisation "idiots".

US President Donald Trump said in August that North Korea possessed 57 "very powerful" nuclear weapons, while South Korea has put the figure at between 80 and 120.