North Korea has fired several projectiles from its east coast, the South Korean military confirmed, as analysts said the country was stepping up pressure against the United States after February's failed nuclear summit in Hanoi.

Key points: South Korea said several short-range projectiles were launched after 9:00am local time (10:00am AEST)

South Korea said several short-range projectiles were launched after 9:00am local time (10:00am AEST) Analysts said the timing of the launch would send a message to the US

Analysts said the timing of the launch would send a message to the US The projectile launches come as the North steps up pressure against Washington following a failed nuclear summit

The South Korean military initially said there had been a missile launch, but subsequently gave a more vague description.

South Korea's joint chiefs of staff (JCS) said Korea and US authorities were analysing details of the launch, which happened about 9:00am local time (10:00am AEST).

In statement the JCS said the North had fired several unidentified projectiles from north of the city of Wonsan that flew between 70 and 200 kilometres.

Earlier South Korea's military command had said the North fired an "unidentified short-range missile".

The firing comes amid a diplomatic breakdown following the failed summit earlier this year between US President Donald Trump and North Korean leader Kim Jong-un over the North's pursuit of a nuclear arsenal that can target the US mainland.

Prime Minster Scott Morrison has commended Mr Trump's efforts and said he had not unreasonably raised expectations of securing peace in the region.

"He's being very honest that this was going to be difficult," Mr Morrison told reporters in Queensland.

"I would only continue to encourage him to take the steps he is taking to ensure that he brings stability to that part of the world. But it's going to have its setbacks, and it clearly has.

"I think it's a reminder of just the unstable world that we live in today. And the pressures that are out there."

If the unidentified projectiles were missiles, it would be the first missile launch since the North fired an intercontinental ballistic missile (ICBM) in 2017.

That year saw a string of increasingly powerful weapons tests from the North and a belligerent response from Mr Trump that had many in the region fearing war.

Launch will send message to the US

White House Press Secretary Sarah Sanders said the Trump administration was aware of North Korea's actions.

"We will continue to monitor as necessary," she said.

A Pentagon press officer said: "We aren't able to confirm anything at the moment, we are looking in to it."

South Korea's presidential Blue House is "analysing the situation," an official said without elaborating.

Japan's Defence Ministry said in a statement that it had not confirmed the entry of any ballistic missile into Japanese territory.

"At this point, we have not confirmed any situation where Japan's national security would immediately be affected," it said.

Analysts said that no matter what type of projectile was fired, the timing of the launch would send a message to the US.

These short-range projectiles do not appear to violate that self-imposed moratorium, and may instead be a way to register Mr Kim's displeasure with Washington and the state of talks meant to provide sanctions relief for disarmament without having the diplomacy collapse.

North Korea angered by Trump's position on sanctions

Mr Kim recently met Russian President Vladimir Putin in a first-ever summit between the two leaders, aimed at resolving a standoff over Pyongyang's nuclear program.

Mr Putin said the two leaders had "exchanged views on how and what needs to be done so that we can improve the situation", while Mr Kim called the discussions "fruitful" and a "meaningful exchange".

Mr Kim has vowed to no longer test nuclear weapons or ICBMs, but the North has conducted other weapons tests since then.

The missile firing, coming after the North's test of what it called a tactical weapons system, added to the pressure it has exerted on Washington.

"It also seems clear that North Korea is angry over what appears to be a lack of flexibility in the Trump administration's position on relieving sanctions, sticking to a policy of 'maximum pressure'," said Harry Kazianis at the Centre for the National Interest, a think-tank.

Mr Kim has held two summit meetings with Mr Trump, the second in February in Vietnam, but the two leaders failed to make progress on ending the North's nuclear program due to disagreement on weapons dismantlement and sanctions relief.

South Korea's military has bolstered its surveillance in case there are additional weapons launches.

Reuters/AP