North Korean leader Kim Jong-un has reportedly ordered a nuclear weapon be placed in a tunnel in preparation for launch, but his true intentions remain unclear.

US officials believe the launch could happen on Saturday, when the rogue state holds celebrations and parades to mark the birth of former ruler Kim il-Sung, known as the 'Day of the Sun' in North Korea.

Unconfirmed reports on the publicly-funded Voice of America, which cite American officials, claim the placing of the device underground points to an imminent test.

A tweet on The Spectator Index also said commercial satellite imagery points to preparation for a nuclear test at at Punggye-ri in the remote north of the country, where previous nuclear tests have taken place.

Reuters reports foreign journalists visiting North Korea have been told by officials to prepare for a "big and important event" on Thursday, although there were no signs it was directly linked to tensions in the region over the isolated state's nuclear weapons program.

Sydney-based security expert Euan Graham, of the Lowy Institute for International Policy, said the reported preparations for a test are consistent with North Korea's strategy of "going nuclear and going early".

"I'm not surprised about this reported move. It is consistent with their plan of early escalation. But it's important to realise the North Koreans have become very sophisticated in knowing what commercial satellites can view and report."

"It is possible that they are yanking our chains. There is no guarantee it will lead to a test."

The unpredictable natures of US President Donald Trump and North Korean leader Kim Jong-un could easily escalate the crisis.

Mr Graham said Saturday's 105th anniversary of Kim il-Sung's birth was significant but not the only one for North Korea watchers.

"We have the foundation day of the People's Army coming up on April 25 and that will be marked with parades. They have pulled in plenty of the international media for this event."

Mr Graham said it was important to realise that the actions of North Korean leader Kim Jong-un are linked to cementing his domestic position.

"With the large American naval force off his waters, he may feel he has to appear assertive to shore up his position within North Korea."

The aircraft carrier USS Carl Vinson is leading a naval task force off the shores off the Korean peninsula.

Mr Graham said the intervention by Chinese president Xi Jinping in urging a "peaceful resolution to tensions" was to give Kim breathing space.

But the unpredictable characteristics of Kim and US President Donald Trump could easily escalate the crisis.

"Does he [Kim] lay low in the face of the Americans or play chicken and detonate a test device."

Defence Industry Minister Christopher Pyne has welcomed China "stepping up to the mark" to pressure rogue state North Korea to behave itself.

Mr Pyne said the responsibility to rein in North Korea mostly rests with China - "the Hermit Kingdom's closest ally" since the 1960s.

"The Chinese Government has overnight stepped up to the mark and is putting pressure on North Korea to ensure it behaves itself," he told reporters in Adelaide on Thursday.

Tensions have escalated on the Korean peninsula, with talk of US military action gaining traction following its strikes against Syria last week, while there are concerns the North may soon conduct a sixth nuclear test.