This picture taken on April 6, 2013 shows a Chinese border guard standing on a look out post by the bridge that crosses the Yalu river to the North Korean town of Sinuiju across from the city of Dandong. - 

China’s new president Xi Jinping is a busy guy. He’s inherited a massive economy with a lot of problems. And now, next door, threats of Armageddon from a man the Chinese have nicknamed ‘Fat Little Kim.’ Over the weekend at an international conference, President Xi said nobody should be allowed to throw the world into chaos for selfish gains. It was the latest sign that China is growing annoyed by Kim Jong-un’s antics.

“I sense them coming to a kind of crunch point," says William McCahill, a former U.S. diplomat in Beijing who is now managing director of Religare Capital. “I know from my own conversations with Chinese officials that they warned the North Koreans in the strongest possible terms not to detonate the third nuclear test, and the Koreans went ahead and did that. The Chinese were absolutely livid."

A volatile North Korea is a big distraction for Xi Jinping. He’s been trying to focus on tough changes at home: Reforming China’s economy by seizing power from state-run companies. “A move against those (companies) is going to require all the political capital he can muster,” says McCahill.

The worst-case scenario for China would be war on the Korean peninsula. "The result would be a flood of North Korean refugees streaming over the border into China. That would be bad for China’s economy," says Cai Jian, a Korean studies professor at Fudan University.

North Korea has always been a buffer state between China and South Korea. A toppled regime in Pyongyang would also mean an important American ally with U.S. military support would suddenly be on China’s doorstep.

Follow Rob Schmitz at @rob_schmitz