Every day two bullet trains race from Beijing to Dandong, on China’s border with North Korea, at speeds approaching 250 kilometres per hour. If the line continued south, they could reach Pyongyang within one hour and Seoul within two.

While such cross-border links are planned with China’s neighbours in south-east and central Asia, in Dandong they remain a fantasy as Sino-US tensions build over North Korea’s nuclear and missile programmes. During a visit to the demilitarised zone separating North and South Korea on Monday, US vice-president Mike Pence urged Beijing to use its “extraordinary levers” over Kim Jong Un’s regime in Pyongyang.

One such lever is just a short walk from Dandong’s high-speed rail station. Built by the Japanese Imperial Army in 1943, the China-Korea Friendship Bridge across the Yalu river is an economic lifeline for Mr Kim. Despite China’s apparent compliance with UN sanctions on selected North Korean exports such as coal, the value of China’s trade with its isolated neighbour increased almost 40 per cent in the first quarter of this year, reflecting sharp increases in global commodities prices.