Tan Rufeng, manager of a Chinese trading company just across the border from North Korea, is not sure whether to blame “old America or young Kim”, the North Korean leader, for the sudden downturn in her fortune. “I don’t understand politics,” she says.

But she does understand the complex business of selling trucks made in China, the world’s fastest-growing big economy, to buyers in North Korea, the world’s most isolated state. Booming until late last year, shipments have slowed dramatically since then, she says from her office in the Hongcheng Trading Company in Dandong, a city of 2.4m people.

“We had been selling scores of these every month,” Ms Tan says, pointing to a sign with dump trucks, earth diggers, fuel tankers and street-sweeping vehicles. “Now we’re doing well if we can sell five. They no longer have money to buy anything.”