China hosts Japan, S Korea amid 'Christmas gift' threat from nuclear North

China hosted the leaders of squabbling neighbours South Korea and Japan on Tuesday, flexing its diplomatic muscle with America's two key military allies in Asia and seeking regional unity on how to deal with a belligerent North Korea.

The gathering in the southwestern city of Chengdu was held with the clock ticking on a threatened "Christmas gift" from North Korean leader Kim Jong Un that would reignite global tensions over its nuclear programme.

Kim has promised the unidentified "gift", which analysts and American officials believe could be a provocative missile test, if the United States does not act make concessions in their nuclear talks by the end of the year.

At the opening ceremony with South Korea's Moon Jae-in and Japans Shinzo Abe on Tuesday morning, Chinese Premier Li Keqiang said he hoped cooperation among their nations would "protect the region's safety and stability".

South Korean President Moon Jae-in said it was important they worked together at a "turbulent" time.

The gathering in Chengdu will feature the first one-on-one meeting between Moon and Japanese Prime Minister Shinzo Abe for 15 months.

Ties between their two nations have hit rock bottom in recent months over trade issues and other disputes related to decades of bitter wrangling over Japan's 1910-45 occupation of the Korean peninsula.

The United States has frequently urged its two allies to bury the hatchet, worried that their poor relations were complicating diplomacy in Asia -- although it has held off on direct mediation.

China is appearing to fill that void with its Chengdu event.

"As the region's major power, China hopes to show its diplomatic presence to the world by bringing the Japanese and South Korean leaders to the same table," Haruko Satoh, professor and expert on Chinese politics at Osaka University, told AFP.

At separate lead-up meetings in Beijing on Monday with Chinese President Xi Jinping, Moon and Abe both spoke of China's hefty diplomatic influence in the region.

Long-running efforts to contain North Korea's nuclear programme have been largely deadlocked since the collapse of a second summit between US President Donald Trump and Kim in Hanoi at the start of this year.

In an effort to pressure the United States, the North has conducted a series of short-range missile tests and threatened to go further with its "Christmas gift".

If the North fired an intercontinental ballistic missile in defiance of UN sanctions, it would destroy Trump's argument that he had succeeded in reducing risks from North Korea.

Former US national security adviser John Bolton, who was dismissed in September, on Monday criticised Trump's strategy and warned the North posed an "imminent" threat.

"The risk to US forces & our allies is imminent & more effective policy is required before NK has the technology to threaten the American homeland," tweeted Bolton.

If the North does carry through with a threatened provocation, the United States should admit its policy of engaging the North had failed, Bolton said in an interview with news site Axios.

The US should then work with allies to show that "when we say it's unacceptable, we're going to demonstrate we will not accept it," he added.

Before leaving for China, Abe told reporters that links with Seoul remained "severe", though the Chengdu meeting was important given the regional issues at stake.

"Considering the security environment in East Asia, I recognise that relations between Japan and South Korea as well as relations among Japan, the US and South Korea are important," he said.

The relationship between Japan and South Korea is overshadowed by the 35 years of brutal colonisation by the Japanese -- including the use of sex slaves and forced labour -- that is still bitterly resented today.

Ties began a downward spiral in recent months after a series of South Korean court rulings ordering Japanese firms to compensate wartime forced labour victims.

These infuriated Tokyo, who insisted the matter had been settled by a 1965 treaty between the two countries.

Seoul then threatened to withdraw from a key military intelligence-sharing pact, although it reversed course in November and agreed to extend it "conditionally".