Kerry presses China to help end N. Korea tensions

China said Saturday it was in everyone's interest to defuse Korea tensions as US Secretary of State John Kerry lobbied for a firmer stand on North Korea at a "critical" juncture for world peace.

Over a long day of diplomacy in Beijing, Kerry warned Chinese leaders including President Xi Jinping that the stakes were high as China's erratic ally North Korea threatens a missile launch that would extend a weeks-long crisis.

The region has been engulfed by threats of nuclear war by Pyongyang in response to UN sanctions imposed over its recent rocket and nuclear tests, and Kerry stressed that China has a unique sway over North Korea.

"Mr President, this is obviously a critical time with some very challenging issues," Kerry told Xi in the Great Hall of the People, on the second leg of an Asian tour that has been swamped by the Korea crisis.

As well as "issues on the Korean peninsula", he cited Iran's nuclear ambitions, Syria and the Middle East, and the world's economic woes.

But there was no sign in public of China endorsing a get-tough approach towards North Korea, with its top diplomat going no further than agreeing with Kerry to pursue a deeper dialogue.

"To properly address the Korean nuclear issue serves the common interests of all parties," Chinese State Councillor Yang Jiechi said ahead of a formal dinner with Kerry.

"It is also the shared responsibility of all parties," added Yang, who is in charge of Beijing's foreign policy. "China will work with other relevant parties including the United States to play a constructive role," he said.

Neither official gave details of any concrete measures that had been agreed. But Kerry said they would have "further discussions to bear down very quickly with great specificity on exactly how we will accomplish this goal".

The secretary of state flew in from talks in South Korea with President Park Geun-Hye, where he offered public support for her plans to initiate some trust-building with the North.

Washington is seeking to persuade Beijing to help rein in the bellicose threats from North Korean leader Kim Jong-Un, and bring Pyongyang back to the negotiating table over its suspect nuclear programme.

"I think it's clear to everybody in the world that no country in the world has as close a relationship or as significant an impact on the DPRK (North Korea) than China," Kerry said Friday in Seoul.

Beijing has backed Pyongyang since the 1950-53 Korean War and could wield tremendous leverage over the isolated communist regime thanks to the vital aid it provides, including almost all of its neighbour's energy imports.

But analysts say it is wary of pushing too hard for fear of destabilising North Korea, which could send waves of hungry refugees flooding into China and ultimately lead to a reunified Korea allied with the United States.

Strains in the relationship between the United States and China, the world's top two economies, have been simmering on an array of diplomatic fronts such as Syria and Iran, as well as trade.

The US Treasury Department on Friday said China's yuan currency remains "significantly undervalued" but stopped short of accusing Beijing of manipulating the currency to gain an unfair trade advantage.

In opening remarks in the presence of reporters, Xi did not mention Korea but said the China-US relationship was "at a new historical stage and has got off to a good start" since his ascension as head of state last month.

But in a commentary issued minutes later, China's official Xinhua news agency said America's strategic "pivot to Asia" could breed mistrust, and Washington should "help seek reasonable and workable solutions to regional issues".

"While accusing Pyongyang of reckless provocation and intolerable disregard of international wishes, Washington itself has also been fanning the flames," it said, citing a recent US military buildup in support of South Korea.

China is estimated to provide as much as 90 percent of North Korea's energy imports, 80 percent of its consumer goods and 45 percent of its food, according to the US-based Council on Foreign Relations.

Despite intelligence reports that the North is ready to stage a highly provocative medium-range missile launch, Park has in recent days made some conciliatory overtures, saying the South should meet with the North.

While Kerry berated Pyongyang's "unacceptable" rhetoric and warned that any missile launch would be a "huge mistake", he also stressed US backing for Park's initiative.