Japan, South Korea and the United States on Saturday ratcheted up pressure on China to support the "strongest possible" punishment against North Korea, following Pyongyang's nuclear test earlier this month.

Japan's Vice Foreign Minister Akitaka Saiki, US Deputy Secretary of State Antony Blinken and their South Korean counterpart Lim Sung-Nam held a one-day meeting at a Tokyo guesthouse, where they called on Beijing to support a strong UN Security Council resolution targeting Pyongyang.

"We strongly hope that China, as its neighbour and the most influential country on North Korea, will fully cooperate with the international community to adopt a strong resolution," Saiki told a joint news conference.

Saiki said the three countries are aiming to help adopt a UN resolution with the "strongest possible contents at the earliest timing".

China, a permanent member of the United Nations Security Council, is North Korea's economic benefactor, but traditional ties have become strained as Beijing's patience has worn thin with Pyongyang's behaviour and unwillingness to rein in its nuclear weapons ambitions.

But China's leverage over Pyongyang is mitigated, analysts say, by its overriding fear of a North Korean collapse and the prospect of a reunified, US-allied Korea directly on its border.

"It's our expectation along with our colleagues... that China will demonstrate a real leadership at the Security Council with us in assuring that there are significant consequences for North Korea's actions," Blinken said.

"The bottom-line is that the failure to take significant measures now almost guarantees that North Korea will continue to repeat this exercise of testing nuclear weapons," he added.

The call came after South Korean President Park Geun-Hye on Wednesday also urged the international community, and in particular China, to back harsh sanctions targeting Pyongyang over the nuclear test.

North Korea says its latest nuclear test was of a miniaturised hydrogen bomb -- a claim largely dismissed by experts who argue the yield was far too low for a full-fledged thermonuclear device.

But whatever the nature of the device, it was North Korea's fourth nuclear test since 2006, and further evidence of Pyongyang's intention to continue developing its nuclear weapons capability in the face of international censure.

S. Korea, China defence officials discuss N. Korea nuclear test
Seoul (AFP) Jan 15, 2016 - South Korean and Chinese defence ministry officials discussed North Korea's latest nuclear test on Friday, as pressure intensified on Beijing to take a tougher line with ally Pyongyang.

The director-level defence talks are held every year, but were completely overshadowed this time around by the North's fourth nuclear test last week, which triggered global condemnation and the promise of fresh UN sanctions.

"China expressed its willingness to take part in adopting a UN Security Council sanctions resolution," the head of the South Korean delegation, Yoon Soon-Ku, told reporters afterwards.

"China reiterated that it thoroughly rejects the North's nuclear development and nuclear testing," Yoon said.

The talks came two days after South Korean President Park Geun-Hye urged China to step up to the plate and support genuinely punitive sanctions that would help bring Pyongyang to heel.

"I believe China is aware that if its strong determination is not put into actual, necessary actions, we will not be able to prevent a fifth or sixth nuclear test," Park said.

China is North Korea's chief diplomatic protector and economic benefactor, but traditional ties have become strained as Beijing's patience has worn thin with Pyongyang's behaviour and unwillingness to rein in its nuclear weapons ambitions.

But China's leverage over Pyongyang is mitigated, analysts say, by its overriding fear of a North Korean collapse and the prospect of a reunified, US-allied Korea directly on its border.

US Secretary of State John Kerry has also urged China to take a stronger line with North Korea, warning in a call to his Beijing counterpart last week that it can no longer be "business as usual".

North Korea says the January 6 test was of a miniaturised hydrogen bomb -- a claim largely dismissed by experts who argue the yield was far too low for a full-fledged thermonuclear device.

But whatever the nature of the device, it was North Korea's fourth nuclear test since 2006, and further evidence of Pyongyang's intention to continue developing its nuclear weapons capability in the face of international censure.

Since taking office in early 2013, Park Geun-Hye has actively courted closer ties with Beijing, and sought to build a personal working relationship with President Xi Jinping.

The two leaders have held numerous summits, and Park was the only leader among major US allies to attend a mass military parade in Beijing to mark the 70th anniversary of the end of World War II.

But while relations have warmed, the North Korean issue remains an extremely delicate one for China, and South Korea will be wary of pushing Beijing too far and too fast.