For years, China has played a spoiler role in negotiations over sanctions on North Korea’s nuclear programme, and is accused of both weakening UN resolutions and failing to police sanctions-busting by Chinese companies.

But on Saturday Beijing surprised analysts with a bold move to ban coal imports from North Korea until the end of the year, raising the question of whether that signals a temporary irritation with Pyongyang, a sea change in strategy towards its neighbour, or something else entirely.

Few believe China wants to wreak serious economic havoc on North Korea. While the US has made little secret it would like to see regime change in Pyongyang, Beijing insists its goal of North Korean de-nuclearisation should not come at the cost of instability or regime collapse. These might trigger a flow of refugees into China or unification of the Korean peninsula under a pro-US government, which is anathema to China’s Communist government.