It has been decades since American bombs rocked Dandong, the main crossing on the 800-mile Chinese-North Korean border. But this week another explosion shook China and the new threat is from its old ally. North Korea's nuclear test has raised tensions throughout the region – and increased pressure on China to rein in its neighbour.
China provides as much as 90% of the North's energy and 40% of its food. Like Russia, it has used its security council veto against attempts to isolate Pyongyang. Without its support, its poor neighbour would struggle to survive.
But now it appears that the North may be exhausting Beijing's patience. This week's nuclear and missile tests, last month's rocket launch, increasing threats and the suspected restarting of the Yongbyon nuclear plant have reignited debate about how best to deal with a troublesome neighbour.
Beijing was swift to slap down the nuclear test in a rare act of public criticism and the US appears hopeful that it will sign a security council resolution toughening existing sanctions – agreed in 2006, but only loosely enforced
"This time, North Korea has gone too far," said Zhang Liangui, a Korea expert at Beijing's Central Party School, which trains Communist party officials. "What they have done has hurt its relationship with China." The Guardian