North Korea has fired what appears to be a submarine-launched ballistic missile off its east coast, South Korea says, amid concerns it might conduct a nuclear test or a missile launch ahead of a key ruling party meeting in May.

Key points: South Korea says North launched missile off its east coast

South Korea says North launched missile off its east coast UK foreign minister says move a "blatant disregard" for international obligations

UK foreign minister says move a "blatant disregard" for international obligations Concerns Workers' Party meeting in early May will trigger more nuclear tests

The North fired the missile to the north-east from an area off its east coast around 6:30pm (local time), the South's office of the Joint Chiefs of Staff said.

The missile flew for about 30 kilometres, a South Korean Defence Ministry official said, adding its military was trying to determine whether the launch may have been a failure for unspecified reasons.

South Korea's Yonhap news agency said the missile flew "for a few minutes", citing a government source.

UK Foreign Minister Philip Hammond said the test showed North Korea's "blatant disregard" for its international obligations, while the US described it a "clear violation" of UN Security Council resolutions.

"Launches using ballistic missile technology are a clear violation of multiple UN Security Council resolutions," State Department spokesman John Kirby said.

North Korea responded by saying it was willing to stop its nuclear weapons tests if the United States suspends annual war games with South Korea.

"I don't know how the US government will consider what I just said but if we continue on this path of confrontation then this will lead into a very catastrophic result, not only for the two countries but the whole entire world as well," North Korean Foreign Minister Ri Su Yong said.

The North will hold a congress of its ruling Workers' Party in early May for the first time in 36 years, at which its leader Kim Jong-un is expected to say the country is a strong military power and a nuclear state.

It first attempted a launch of the submarine-based missile last year and was seen to be in the early stages of developing such a weapons system, which could pose a new threat to its neighbours and the United States if it is perfected.

However, follow-up test launches were believed to have fallen short of the North's expectations as its state media footage appeared to have been edited to fake success, according experts who have seen the visuals.

South Korea's military has said it was on high alert over the possibility that the isolated North could conduct its fifth nuclear test "at any time" in defiance of UN sanctions after setting off what it said was a hydrogen device in January.

North Korea is banned from nuclear tests and activities that use ballistic missile technology under UN sanctions dating back to 2006 and most recently adopted in March but it has pushed ahead with work to miniaturise a nuclear warhead and develop an ICBM.

A senior US official said this week that North Korea should take a lesson from Iran, which has agreed to roll back its nuclear program in an agreement with Western powers in return for lifting of major sanctions.

But the North has shown no sign of entering into such a pact.

Reuters