US Secretary of State John Kerry and Chinese Foreign Minister Wang Yi agreed on the need for a significant new UN Security resolution targeting North Korea after its nuclear test.

Kerry, on a two-day visit to Beijing, had been expected to press China, North Korea's lone major backer, for more curbs on Pyongyang after it said it had successfully conducted a test of a miniaturised hydrogen nuclear device, though the United States has voiced scepticism as to whether it was that powerful.

China has insisted it is already making great efforts to achieve de-nuclearisation on the "Korean peninsula" and Wang rejected any "groundless speculation" on its North Korea stance, following remarks from U.S. officials that China could do more.

"We agreed that the U.N. Security Council needs to take further action and pass a new resolution," Wang told reporters at a joint briefing with Kerry.

"In the meantime, we must point out that the new resolution should not provoke new tensions."

Kerry said the two sides had agreed to an "accelerated effort" at the U.N. to reach a "strong resolution that introduces significant new measures" to curtail North Korea's ability to advance its nuclear and ballistic missile programs.

"It's not enough to agree on the goal. We believe we need to agree on the meaningful steps necessary to get the achievement of the goal," Kerry said.

The exchange of goods and services between China and North Korea was one area where steps could be taken to pressure Pyongyang back to talks, he said.

Kerry also said that shipping, aviation, trade of resources, including coal and fuel, and security at border customs, were key areas in the sanctions debate. North Korea is heavily reliant on China for oil, gasoline and trade.

"All nations, particularly those that seek a global leadership role, share a fundamental responsibility to meet this challenge with a united front," Kerry said.

He added that the US would take "all necessary steps" to honour security commitments to allies, signalling that the U.S. was prepared to continue ramping up its military presence in the region, a move that would likely unsettle Beijing.

"North Korea poses an overt threat, a declared threat, to the world, and it has stated its intention to develop a thermonuclear weapon," he said. "In addition, it has made clear its intent to develop an intercontinental ballistic missile with the capacity to carry a nuclear warhead."

The 15-member UN Security Council said at the time of North Korea's test that it would begin working on significant new measures in response, a threat diplomats said could mean an expansion of sanctions.

Since then, diplomats said Washington and Beijing have been primarily negotiating on a draft resolution, but when asked on Saturday if they were nearing agreement, US Ambassador to the United Nations Samantha Power said no.

After talks yesterday, which went hours past schedule, Kerry said details still had not been set.

In a sign that Beijing could be reluctant to take a more hardline stance on North Korea, state news agency Xinhua said it was "unrealistic to rely merely on China to press the DPRK to abandon its nuclear programme, as long as the U.S. continues an antagonistic approach wrought from a Cold War mentality".

"Bear in mind that China-DPRK ties should not be understood as a top-down relationship where the latter follows every bit of advice offered by the former," Xinhua said, referring to North Korea by its official name, the Democratic People's Republic of Korea.

Xinhua commentaries are not official government pronouncements, but can be read as a reflection of official thinking. Wang added that sanctions should be seen as a path to negotiation, and not as a punitive end in themselves