If North Korea launches a rocket into space or conducts a nuclear test in the coming weeks, as observers suspect it may, China is certain to respond angrily, and perhaps with an unprecedented level of economic punishment.
The question is whether North Korea can be swayed even by its most important ally.
China, which fought on North Korea's side in the 1950-53 Korean War and remains its biggest trading partner and source of assistance, is thought to have the most leverage of any nation over Kim Jong Un's authoritarian country.
Yet the degree of that influence has long been questioned, particularly over the almost four years since Kim took power following the death of his father, Kim Jong Il, who visited China repeatedly and maintained close ties with Beijing.
Kim the younger has yet to make a trip to China or receive any high-ranking Chinese officials in Pyongyang. He snubbed a prestigious military parade in Beijing earlier this month by instead sending an envoy, secretary of the ruling Korean Workers Party Choe Ryong Hae.
Now, North Korean officials have signaled that they could mark the 70th anniversary of the founding of its ruling Workers Party on October 10 with a satellite launch, and announced a restart of atomic-fuel plants that prompted speculation that it is preparing for its fourth nuclear test explosion.
Either a nuclear test or a satellite launch would violate UN resolutions, the latter because the rocket technology needed can also be used to develop long-range missiles.
China's response to North Korea's last declared nuclear test, in the spring of 2013, was considered something of a watershed in degree of harshness.
China swiftly joined the international community in condemning the action, called in the North Korean ambassador to protest, and, according to some indications, slowed the flow of goods across their border.
A new nuclear test or rocket firing could lead China to enforce existing and future sanctions more vigorously.
"China will strongly oppose (a test or launch) and will be sure to implement future United Nations resolutions even more resolutely," said Zhang Liangui, a North Korea expert with the ruling Communist Party's main research and training institute in Beijing.
China may also take unilateral steps such as cutting back on cross-border trade, Chinese experts say. Such measures could target the industrial commodities and luxury goods Kim needs to keep the moribund North Korean economy ticking over and ensure the loyalty of regime supporters.
