The escalation of North Korea’s nuclear and missile programme has dealt a blow to an already beleaguered group of Chinese experts who advocate a softer approach to Beijing’s unpredictable neighbour.

Arguing that sanctions are counterproductive, and military action unthinkable, a dominant group of Chinese academics has long insisted that the only way through the crisis will be to build economic bridges with Pyongyang and even acquiesce to North Korea as a nuclear state.

But this viewpoint is getting harder to sustain, the more nuclear tests shake the ground in China’s northeastern provinces. Pyongyang’s actions, and the regime’s escalating rhetoric, have infuriated Beijing, which has staked its credibility on being able to handle Kim Jong Un, North Korea’s leader. The hydrogen bomb test on Sunday — the biggest yet — caused earth tremors deep inside Chinese territory.

China’s “expert community” is the best window into the country’s largely opaque foreign policy machine. Gradually this year, voices sympathetic to North Korea have disappeared from newspaper op-eds and academic journals.

“They’re out there,” Paul Haenle, director of the Carnegie-Tsinghua Center for Global Policy, a think-tank, said of those in China who continue to urge for a soft stance on North Korea, “but they’re getting less and less.”

Instead, China’s North Korea hawks are emerging. While Beijing’s official statements tend to stick to anodyne talking points, China’s academics and think-tank experts are increasingly talking of the need to get tough with Pyongyang.

“The sanctions imposed on North Korea are still lacking strength and global scale,” Zhang Liangui, professor at the Chinese Communist party’s Central Party School in Beijing, said in an interview on Tuesday. “The sanctions are ineffective and not powerful enough.”

Only recently such a view might have elicited a public slap-down. When Prof Zhang’s pro-sanctions views were raised at a press briefing in April, the foreign ministry replied that “you should only listen to the Chinese government on such questions”.

Now, however, the dovish voices are being squeezed out, said James Reilly, professor at Sydney University and author of an upcoming book on Chinese economic statecraft. “This group is shrinking, while the group that thinks it would be a good idea to toughen up sanctions [is] getting larger.”

The Global Times, China’s nationalistic state newspaper, became another sanctions hawk in April when it raised the idea in an editorial of curbing oil supplies to North Korea, though it stopped short of endorsing a full embargo. On Sunday it said more stringent UN sanctions were “inevitable” following the latest nuclear test.

Zhu Feng, director of the Institute of International Studies at Nanjing University, said in the July issue of the US journal Foreign Affairs: “Now is the time for China to be utterly comprehensive, to seal all the cracks and thus send a clear signal to North Korea”.

The debate among these experts is virtually the only public discussion in China of one of the country’s biggest foreign policy issues. Social media is scrubbed of any mention of North Korea, and newspapers are discouraged from quoting all but the most official voices. Official thinking is conducted entirely behind closed doors.

For years, Beijing has supported gradually increased UN sanctions on Pyongyang, while acting as a brake on Washington’s desire for more punishing measures.

China, through which 90 per cent of North Korea’s trade passes, argues that tougher sanctions threaten to cause a social crisis or the collapse of the North Korean regime. While many in the west would cheer such a development, for China it would mean a humanitarian catastrophe on its border and loss of a key buffer state if the Korean Peninsula unified. Many experts have echoed the view that economic development would make North Korea less belligerent and a better neighbour.

When China last year tightened sanctions on Pyongyang, a number of experts openly questioned the approach. Zhang Shou, a professor at Yanbian university, described North Korea in an academic paper as a “weapon” and a “chip that China can play in dealing with the US and other countries”.

Wang Junsheng, a member of the Chinese Academy of Social Sciences, advocated “all kinds of methods to improve our common development with North Korea”, including increasing foreign assistance and welcoming Pyongyang into the Beijing run Asian Infrastructure Investment Bank.

Meanwhile, Cui Lei, a researcher at the China Institute of International Studies, a foreign ministry think-tank, wrote an article in a Singapore newspaper arguing that North Korea should be allowed into the nuclear club. “It’s now pointless to deny that North Korea has gone nuclear,” he wrote. “We should re-adopt our India-Pakistan approach: acquiescence in North Korea’s nuclearisation, while refusing to legalise it.”

Now a change in the expert voices seems to signal a shift. Susan Shirk, chair of the 21st century China Center at the University of California in San Diego, said before the latest test: “There is a growing gap between academic analysts who are ready to cut Pyongyang loose and the government that still is trying to preserve the relationship with the Kim regime by not putting too much pressure on it”.

However, few are under any illusions that the counsel of expert voices will sway China’s government. Mr Haenle cautioned: “It’s the politics that will decide this, not expert arguments”.