A North Korean missile "blew up almost immediately" on its test launch today, the US Pacific Command said, hours before US Vice President Mike Pence was due in South Korea for talks on the North's increasingly defiant arms programme.

The failed launch from North Korea's east coast, ignoring admonitions from major ally China, came a day after North Korea held a military parade in its capital, marking the birth anniversary of the state founder, in which what appeared to be new long-range ballistic missiles were on display.

South Korea said the combined show of force "threatened the whole world".

Pence is due in Seoul at the start of a 10-day trip to Asia in what his aides said was a sign of the US commitment to its ally in the face of rising tension.

The US nuclear-powered USS Carl Vinson aircraft carrier strike group is also heading to the region.

A US Navy attack on a Syrian airfield this month with Tomahawk missiles raised questions about US President Donald Trump's plans for reclusive North Korea, which has conducted several missile and nuclear tests in defiance of U.N. sanctions, regularly threatening to destroy the South and the United States.

South Korea, which hosts 28,500 US troops, warned of punitive action if the launch led to further provocations such as a nuclear test or a long-range missile launch.

"North Korea showing a variety of offensive missiles at yesterday's military parade and daring to fire a ballistic missile today is a show of force that threatens the whole world," South Korea's Foreign Ministry said in a statement.

TIMING SIGNIFICANT

The North has warned of a nuclear strike against the United States if provoked. It has said it has developed and would launch a missile that can strike the mainland United States but officials and experts believe it is some time away from mastering the necessary technology.

The US Pacific Command said the missile "blew up almost immediately", adding the type of missile was being analysed.

"The North attempted to launch an unidentified missile from near the Sinpo region this morning but it is suspected to have failed," South Korea's Office of the Joint Chiefs of Staff said in a statement.

There was a high degree of confidence it was not an intercontinental ballistic missile, a US official said on condition of anonymity. A second US official said the launch was land-based.

The timing of the test, coinciding with Pence's trip and a day after the military parade, would suggest deliberate defiance.

Pence had been briefed on the failed launch en route to Seoul and had been in touch with Trump, White House aides said.

The North launched a ballistic missile from the same region earlier this month ahead of a summit between the United States and China to discuss the North's arms programme.

That missile flew about 60 km (40 miles) but what US officials said appeared to be a liquid-fuelled, extended-range Scud missile only travelled a fraction of its range before spinning out of control.

China has spoken out against North Korea's missile and nuclear tests and has supported U.N. sanctions. China on Friday again called for talks to defuse the crisis.

Its national airline, Air China, has cancelled some flights to the North Korean capital, Pyongyang, due to poor demand but it has not suspended all flights there, it said on Friday.

Hong Kong's South China Morning Post said on Sunday that state-owned China International Travel Services, Ctrip.com International – China’s main online travel website – and many other Chinese operators had halted travel to North Korea.

Sinpo, where the Sunday launch took place, is the site of a North Korean submarine base and where the North has tested the submarine-launched ballistic missile it is developing.

“It appears today’s launch was already scheduled for re-launching after the earlier test-firing,” said Kim Dong-yub, a military expert at Kyungnam University's Institute of Far Eastern Studies in Seoul.

“This launch can possibly be a test for a new type of missile or an upgrade."

Tension had escalated sharply in the region amid concerns that the North may conduct a sixth nuclear test or a ballistic missile test launch around Saturday's birth anniversary of founding father Kim Il Sung that it calls the "Day of the Sun".

The White House has said Trump has put the North "on notice".

MISSILE TEST? WHAT TEST?

Impoverished North Korea and the rich, democratic South are technically still at war because their 1950-53 conflict ended in a truce, not a peace treaty.

Chinese tourists in Dandong, a city bordering North Korea, piled on to ferries and speedboats on Sunday for cruises on the Yalu river and up-close views of North Korean border guards and villages.

Tourist Huang Xiaojie said North Korea did not have the military ability to go to war.

"North Korea is just trying to gain more attention and gain more leverage," he said.

In Pyongyang, there was a festive atmosphere at a flower show, with families out, taking pictures with North Korean-made smart phones. There was no mention of the test failure on the KCNA state news agency.

Company worker Rim Chung Ryol, 30, said he had not heard of the missile test.

"If it is a failure, then failure is the mother of success," he told Reuters. Asked if he believed international media reports, he said no, because "international media often lies and reports negative news about North Korea".

Factory worker Ri Gul Chol, 37, enjoying the exhibition with his wife and child, also had not heard about the missile test.

"But whatever Kim Jong Un decides and instructs will succeed and all the citizens will support him," he said, referring to the North's young leader.