China faces a chorus of demands from Washington and its regional allies, South Korea and Japan, to bring to heel its friend North Korea after Pyongyang shelled a South Korean island, triggering a volatile confrontation.
But just how much influence over North Korea does Beijing wield and will it use it? Here are some answers:
HOW MUCH INFLUENCE DOES CHINA HAVE OVER NORTH KOREA?
In theory, China has more influence over North Korea than any other power. It is the closest the North has to an ally.
China's new Communist government came to the aid of North Korean Communist forces in the war of the 1950s, and in 1961 the two countries signed a pact that calls for either to aid the other if attacked. It remains in force, although its application is unclear.
China also supplies North Korea with much-needed oil, food and other essentials, all the more important since Pyongyang's relations with South Korea have worsened.
From January to October this year, China shipped a total of 447,278 tonnes of crude oil to North Korea, a rise of 3.7 percent on the same period last year.
From January to October, as well, China exported 72,550 tonnes of corn and 63,136 tonnes of rice. The rice shipments were up 16.1 percent on the same time last year.
SO WHY DOESN'T CHINA USE MORE OF THAT POTENTIAL SWAY?
Chinese analysts and officials say that their country's relationship with the North is more tense and brittle than outsiders, especially Washington, assume. They have a point.
They argue that too much pressure on North Korea from China could backfire for both efforts at nuclear disarmament and for China's bilateral ties with Pyongyang.
In October 2006, North Korea held its first nuclear test explosion, defying public pleas from Chinese leaders. Beijing is unlikely to risk the humiliation of a similar rebuff.
"We all know that China supplies North Korea with substantial food and oil. It is North Korea's principal trade partner and aid donor. It does have considerable influence on Pyongyang," said Joseph Cheng, a political science professor at the City University of Hong Kong.
"At the same time, there's a limit to what China can do. If China completely cuts off trade and aid, Pyongyang may be destabilized. China may risk totally alienating Pyongyang."
WHAT DOES CHINA FEAR?
China does not want North Korea to possess a nuclear arsenal or to provoke a wider military confrontation with South Korea. At the same time, it wants to avoid domestic upheaval in the North or rupturing bilateral ties with Pyongyang.
China's 1,416-km (880-mile) border with North Korea includes stretches of rivers that freeze over in winter, and in past years thousands of North Korean refugees have crossed over.
For China, the priority is to prop up the North's supreme leader Kim Jong-il rather than risk his regime fracturing and threatening chaos that would spill into its territory and, perhaps, lead to South Korea and its ally the United States moving right up to its border.
Worries about what could follow Kim's death or infirmity appear to have magnified China's determination to consolidate its stake in the North.
North Korea has entered a potentially long, unpredictable leadership transition, with the elevation of Kim's youngest son, Kim Jong-un, in September to the rank of general -- a clear sign he is the chosen successor.
Chinese analysts have said their government wants to ensure that it has ties to Kim Jong-un and other emerging leaders, and confrontation would make that difficult.
WHAT IS CHINA LIKELY TO DO?
Beijing will probably at most chide Pyongyang and urge restraint by all.
It could also tighten enforcement of U.N. sanctions on exports of luxury goods and arms to North Korea, but will resist demands for broader sanctions that would threaten its bonds with the North.
When the North's Kim Jong-il visited China in May, Chinese reports said Chinese President Hu Jintao told Kim that their two countries should "strengthen strategic communication" on major domestic and foreign issues. So there may be an opening.
"China may send a special envoy to Pyongyang to push them to exercise restraint," said City University of Hong Kong's Cheng.