Mr Kim is notoriously opaque (as well as afraid of flying). It is not clear whether he accepted the invitation — or whether he has learnt from the experience. But it is clear, with the world on notice that Pyongyang is indeed planning a nuclear test, and Beijing pleading for calm, that the North Korean crisis is now more acute than ever.

The chief culprit in this emergency is North Korea itself. This bears emphasising because Mr Kim’s barbaric regime is so reluctant to engage with its neighbours, and so unreliable when it does, that the heavy lifting in the search for regional stability will have be done by others. This is why the international spotlight is now trained even more harshly on Beijing than on Pyongyang.

There are clear humanitarian arguments for providing food aid to a populace whose rulers inflict famine on the many in order to preserve the fortress-like isolation of the very few. But China’s political vacillation towards North Korea is a separate, and self-defeating, matter. It has encouraged North Korea to proceed with its nuclear weapons programme, and to sign deals to relieve the pressure of sanctions, only to renege on them the moment they are signed. It has also emboldened hardliners in Tokyo to demand a strengthened Japanese military, to the consternation of Seoul as well as Beijing.

When Mr Kim authorised the launch in July of a missile with the potential to reach Delhi or Alaska, international condemnation was at first unanimous. Then, at last month’s conference of “non-aligned” (and pariah) leaders in Havana, the Chinese leadership effectively endorsed North Korea’s drive for nuclear power status by condemning a new set of carefully targeted Western sanctions.

Beijing is now urging the wider world not to overreact to Mr Kim’s latest provocation. Given his taste for dangerous theatrics, this may be sound advice — but only if it is accompanied, privately if necessary, by unambigious signals that to proceed with a test would jeopardise the one outside relationship on which North Korea depends. There is no sign that such signals have been sent; nor even of any coherent Chinese policy towards its supremely irresponsible neighbour.

Last year, Pyongyang agreed to suspend nuclear weapons development in return for the suspension of some sanctions, but its delegation failed to appear at follow-up talks. Only China now has the leverage to bring North Korea back from the brink. It has much to gain by accepting its responsibility as the regional power, and the world has much to lose it if does not.