North Korea's sole major ally China will decrease aid to Pyongyang if it goes ahead with a planned nuclear test, state-run media said in an unusually frank warning on Friday.

China is the North's leading energy supplier and trade partner and is seen as one of the few nations able to influence Pyongyang's behaviour, with the comments adding a distinctive edge to its typical official calls for stability and dialogue.

"If North Korea engages in further nuclear tests, China will not hesitate to reduce its assistance to North Korea," the Global Times said in an editorial.

"Just let North Korea be 'angry'. We can't sit by and do nothing just because we are worried it might impact the Sino-North Korean relationship."

The same comments appeared in the Chinese version of the article. The paper is owned by the People's Daily, the official mouthpiece of the ruling party, and normally takes a nationalistic tone on foreign relations.

The editorial came after Pyongyang reacted furiously to a UN Security Council resolution this week condemning its rocket launch last month and imposing expanded sanctions.

It vowed to boost its nuclear arsenal and to conduct a third nuclear test and more long-range rocket launches in an "all-out action" against its "sworn US enemy".

"China has a dilemma: there's no possible way for us to search for a diplomatic balance between North Korea and South Korea, Japan and the US," the Global Times said, seemingly distancing itself from Pyongyang -- while also saying China would "resolutely stop" any "extreme" sanctions.

"We should have a pragmatic attitude to deal with the problems and pursue the optimal ratio between our investment of resources and strategic gains," it added.

"China hopes for a stable peninsula, but it's not the end of the world if there's trouble there."

The editorial also expressed discontent at what it saw as North Korean criticism of Beijing for backing the UN resolution, which only passed after lengthy negotiations between the US and China.

Envoys said Beijing had sought to shield Pyongyang from tougher measures.

"After putting a lot of effort into amendments for the draft resolution, China also voted for it. It seems that North Korea does not appreciate China's effort," the Global Times said.

China's foreign ministry played down the editorial, with spokesman Hong Lei saying it was "only the opinion of the media".

He reiterated the calls for restraint China made after Thursday's announcement from Pyongyang, saying: "We hope parties concerned can exercise calmness, enhance dialogue and refrain from actions that might escalate tension."

China has repeatedly called for the resumption of the six-party talks process, which is chaired by China and also involves the two Koreas, the United States, Japan and Russia.

The aim has been to convince Pyongyang to abandon its nuclear programme in return for aid and security guarantees, but the talks have been moribund since the North left the forum in 2009.