China's unusually forceful criticism of North Korea shows the rising power is eager to distance itself from a pariah, but experts doubt Beijing would ultimately put the regime's survival at risk.

The Global Times, a state-run newspaper close to China's ruling Communist Party, said in an editorial that if North Korea goes ahead with plans to test a nuclear bomb, Beijing "will not hesitate to reduce its assistance."

The newspaper, which normally takes a nationalistic tone on foreign policy, voiced exasperation with North Korea and accused Kim Jong-Un's regime of failing to appreciate China's efforts on its behalf.

North Korea vowed to carry out its third nuclear test after the UN Security Council condemned its December 12 rocket launch. The resolution was a compromise with China, which resisted US calls to impose new forms of sanctions but agreed to put more North Koreans on existing blacklists.

Scott Snyder, a senior fellow at the Council on Foreign Relations, said that China may have concluded that North Korea would respond angrily no matter what and decided, "Why should we take the hit if it's not going to make a difference?"

Snyder said that China may have been upset not as much by the planned nuclear test but by North Korea's simultaneous vow to leave six-nation talks on denuclearization, a main means of Chinese leverage in regional diplomacy.

But Snyder said there was no evidence that China's leadership under president-in-waiting Xi Jinping has conducted a fundamental rethink on North Korea.

"Until there is some evidence of that, I think we have to presume that China's core objective remains stability and that they are still in North Korea's corner, even though North Korea makes it very hard for them," he said.

China is widely seen as fearing the consequences of a North Korean collapse, which could cause an exodus of refugees and potentially lead to a reunified, US-allied Korea directly on its border.

China has been the primary benefactor of Pyongyang since the 1950-53 Korean War, providing critical diplomatic support and economic links to one of the world's most isolated and repressive regimes.

Philip Yun, a former US policymaker on Korea, said that Pyongyang was keenly aware that China did not want the regime to collapse and had likely mapped out the expected reactions to its announcement.

"Quite frankly, the North Koreans know the Chinese are not being nice because they like the North Koreans. The Chinese are doing this because it's in China's interest," said Yun, executive director of the Ploughshares Fund, a group opposed to nuclear weapons.

North Korea has been a perpetual irritant in relations between the United States and China, with US officials demanding that Beijing take stronger action after every crisis.

The US-China relationship has seen turbulence after Secretary of State Hillary Clinton on January 18 strongly supported US ally Japan with a warning to Beijing not to challenge Tokyo's control of disputed islands.

The tone between the Pacific powers was markedly different a week later, with Glyn Davies, the US pointman on North Korea, saying in Beijing that the United States and China had a "very strong degree of consensus."

Yun said that the Chinese wanted a better relationship with the United States and faced a dilemma on North Korea.

"The Chinese are attached, I think, essentially to a loser and they are trying to figure out a way to deal with this that doesn't poison the rest of the relationship" with the United States, Yun said.

James Acton, a nuclear expert at the Carnegie Endowment for International Peace, doubted that pressure could dissuade the North Koreans from carrying out their test.

"I think the North Koreans just say -- how bad can it be? The Chinese have never punished us in a serious way in the past, so why would they do so in the future?" he said.

"It's one thing if the North Koreans haven't made something public -- at that point, extensive private pressure could work. But having made it public, it's very hard to see how anyone -- even China -- can influence North Korea's decision," he said.