DANDONG, China—Beijing on Friday lodged its first official protest of a joint U.S.-South Korean military exercise planned for Sunday, even as the aircraft carrier USS George Washington steamed toward the region. 
 
 North Korea also responded angrily. "The situation on the Korean peninsula is inching closer to the brink of war," the state controlled Korean Central News Agency responded Friday to the maneuvers, which are set to take place in the Yellow Sea between the Koreas and northeastern China. 
 
 Protesters chant anti-North Korea slogans and scuffle with police in Seoul as U.S. and South Korean war game begins. Video courtesy of Reuters. 
 
 The strong talk was the latest fallout from North Korea's hour-long artillery attack of a South Korean island on Tuesday that killed four people. The next day, the U.S. and South Korea said planned joint exercises would go ahead over the weekend, heightening fears in some quarters that already-tense relations between North and South Korea—and their respective international protectors, China and the U.S.—could be heading for a showdown. 
 
 Yet China's outwardly defiant response belies a more delicate political reality: Beijing's continued support of North Korea's erratic, martial regime is beginning to extract real costs. China's statement Friday included a face-saving formulation that appeared to open the door for a scenario China has long sought to avert—a U.S. aircraft carrier, a potent symbol of U.S. military might, plying the edge of Chinese waters. 
 
 China's Foreign Ministry suggested it wouldn't escalate its protests against the naval exercises as long as they took place outside China's "exclusive economic zone," a term of international maritime law for an area where countries enjoy mineral and fishing rights, generally 200 nautical miles from a country's coast. 
 
 View Full Image Associated Press The U.S. military aircraft carrier USS George Washington sets sail from Yokosuka naval base. 
 
 "We hold a consistent and clear-cut stance on the issue," Foreign Ministry spokesman Hong Lei was quoted as saying in a ministry statement. "We oppose any party to take any military actions in our exclusive economic zone without permission." 
 
 The U.S. doesn't announce precise locations for such maneuvers for security reasons. But there are parts of the Yellow Sea, including those near South Korea, that fall outside China's exclusive economic zone, giving the U.S. areas where it can conduct drills without incurring China's wrath. 
 
 China's stance appeared firmer in July, when officials said they opposed any military exercises in the entire Yellow Sea. Beijing protested so vociferously that the U.S. and South Korea shifted planned maneuvers to the Sea of Japan, east of South Korea. 
 
 A History of Korean Tensions A detailed timeline of the recent skirmishes between North and South Korea. View Interactive Photos From the Scene View Slideshow Associated Press A train-station TV screen in Seoul shows smoke pouring from Yeonpyeong island Tuesday. 
 
 China has long frustrated U.S. efforts to bring its nuclear-armed neighbor to heel, fearing any radical change could sow chaos in the region and potentially lead to a unified Korea with a U.S. military presence directly on its border. Beijing refused this week to blame North Korea for Tuesday's attack. Privately, its officials maintain, the weekend's exercises could be a grave mistake that risk further provoking the North. 
 
 But current and former U.S. officials who have worked on North Korea said Friday that they saw China in a growing quandary in how to square its support for Pyongyang with the regime's continued provocations. 
 
 Beijing has sought in recent months to deepen its economic and strategic relationship with North Korea, despite U.S. objections, arguing it would help contain leader Kim Jong Il's nuclear work and military provocations. As Pyongyang has continued to challenge the international community, however, China has been placed in an increasingly weakened position to protest U.S. military action. 
 
 "China is having a much harder time in defending its policy, but they only have themselves to blame," said Michael Green, who oversaw Asia policy for the White House during George W. Bush's first term. "You talk to any Chinese official, and they're furious with the North Koreans." 
 
 Beijing is also facing renewed criticism from Chinese foreign-policy experts, journalists and Internet activists who question whether unqualified support for North Korea is still in China's interests. 
 
 China's apparently softened stance on Yellow Sea exercises appears to demonstrate a concern that the North Korean crisis will overshadow a planned trip to Washington in January by President Hu Jintao. It may also reflect an acknowledgment that China would be unlikely to prevent the U.S. and South Korea from staging their drills following the week's attack, requiring a compromise to avoid appearing weak before an increasingly nationalist and demanding Chinese public. 
 
 U.S. military officials insisted Friday that the exercise scheduled for this weekend shouldn't be interpreted as anything but an attempt to deter North Korea from further attacks on the South. 
 
 "This exercise is not directed at China," said Capt. Darryn James, a Pentagon spokesman. "The purpose is to strengthen the deterrence against North Korea." 
 
 U.S. officials on Friday said the Obama administration continues to focus its diplomacy in Northeast Asia on gaining China's cooperation to exert more pressure on North Korea. 
 
 China also made an attempt Friday to mediate among all sides in the crisis, with U.S. Secretary of State Hillary Clinton speaking by telephone with Chinese Foreign Minister Yang Jiechi. State Department spokesman P.J. Crowley, briefed on the phone conversation, said "the secretary encouraged Beijing to send a clear message that North Korea's behavior is unacceptable." 
 
 Mr. Yang, who also talked with officials from North and South Korea, said he was "worried" by this week's developments, according to a statement from the Foreign Ministry. He urged the two Koreas to stay calm and resolve their differences through negotiations, saying it was important to "control the situation" and avoid further incidents, according to the ministry statement. 
 
 President Barack Obama is expected to speak with Hu Jintao on the North Korea crisis in the coming days, according to U.S. officials. 
 
 The White House declined to comment on China's response so far to the North Korea attack, noting that U.S. consultations with Beijing are ongoing. "The president's conversation with Hu Jintao will be extremely important," said a senior U.S. official. 
 
 The U.S. has been planning a naval exercise in the Yellow Sea since July, when an expanded list of training events was announced in response to the March sinking of the South Korean patrol ship Cheonan, which killed 46 sailors and was widely blamed on the North. 
 
 The July exercises also came after China had objected strongly to a speech by Mrs. Clinton in which she said that the U.S. had a national interest in protecting freedom of navigation in the South China Sea. Ever since, China and the U.S. have been engaged in a tussle for influence in the region, where many Southeast Asian nations that have territorial disputes with China are looking to beef up defense relations with the U.S. 
 
 Since July, military officials have acknowledged that they understand China's concerns with the exercises but have defended their intention to operate in the Yellow Sea. "These exercises will take place in international waters," Pentagon spokesman Capt. James said. "We routinely operate in international waters, east and west of the Republic of Korea." 
 
 "We have been completely transparent with China about our intent to conduct these exercise and their purpose," added a U.S. military official. 
 
 China has challenged U.S. vessels operating in what it considers its economic zone. In March 2009, Chinese vessels harassed the USNS Impeccable, a U.S. vessel staffed with civilians from the military Sealift Command. The Impeccable was in international waters but within China's exclusive economic zone. 
 
 The U.S. last conducted exercises in the Yellow Sea in October 2009. Those drills also involved the USS George Washington. 
 
 One high-level South Korean official said the maneuvers would be off South Korea's southwest coast, far from the disputed maritime border with North Korea. 
 
 Write to Jay Solomon at jay.solomon@wsj.com ||||| China has drawn up detailed contingency plans for the collapse of the North Korean government, suggesting that Beijing has little faith in the longevity of Kim Jong-un’s regime. 
 
 Documents drawn up by planners from China’s People’s Liberation Army that were leaked to Japanese media include proposals for detaining key North Korean leaders and the creation of refugee camps on the Chinese side of the frontier in the event of an outbreak of civil unrest in the secretive state. 
 
 Any senior North Korean military or political leaders who could be the target of either rival factions or another “military power,” thought to be a reference to the United States, should be given protection, the documents state. 
 
 North Korean soldiers patrol the bank of the Yalu River which separates the North Korean town of Sinuiju from the Chinese border town of Dandong, northeast China (Getty) 
 
 According to Kyodo News, the Chinese report says key North Korean leaders should be detained in special camps where they can be monitored, but also prevented from directing further military operations or taking part in actions that could be damaging to China’s national interest. 
 
 The report suggests “foreign forces” could be involved in an incident that leads to the collapse of internal controls in North Korea, resulting to millions of refugees attempting to flee. The only route to safety the vast majority would have would be over the border into China. 
 
 The Chinese authorities intend to question new arrivals, determine their identities and turn away any who are considered dangerous or undesirable. 
 
 “This only underlines that all the countries with a stake in the stability of north-east Asia need to be talking to each other,” Jun Okumura, a visiting scholar at the Meiji Institute for Global Affairs, told The Telegraph. 
 
 “What we have learned from the collapse of other dictatorships – the Soviet Union, Muammar Gaddafi’s Libya – is that the more totalitarian the regime, the harder and faster they fall,” he added. 
 
 “This is why we need contingency plans and I am sure that the US and South Korea have extensive plans in place, but the release of Chinese measures is new,” he said. 
 
 Okumura believes that the timing of the leak of the study is significant, given that China can have been expected to have similar contingency plans in place for the past two decades that North Korea has been teetering on the edge of implosion. 
 
 The release of the study comes just days after Beijing issued a thinly veiled warning to Pyongyang, ahead of a fourth anticipated nuclear test, that China would “by no means allow war or chaos to occur on our doorstep.” 
 
 China, which is North Korea’s sole remaining significant supporter, also refused to export any crude oil over its border to the North in the first three months of the year.
– China is ramping up its military presence on its 880-mile border with North Korea in case a nuclear, economic, or military crisis sends millions of North Koreans fleeing in search of greener pastures, according to government websites. But as the Wall Street Journal reports, that might not be all China is preparing for. China's Defense Ministry hasn't referred to North Korea as the reason for a new border defense brigade along with a 24-hour video surveillance system, unit upgrades, new shelters and command posts, and recent live-fire and special forces drills in border regions; but experts say China could be preparing to intervene should the US attempt to seize nuclear weapons from its ally on the Korean Peninsula. Some aren't so sure China would be keen to take on the US and stress that recent enhancements at the border were first discussed last year. However, "once you start talking about efforts from outside powers, in particular the United States and South Korea, to stabilize the North ... you’re starting to look at a much more robust Chinese response," argues a former US defense official for East Asia. "If you’re going to make me place bets on where I think the US and China would first get into a conflict ... it’s the Korean Peninsula." Others note China will want to prevent US influence there to retain its regional power. In a column in May, retired Maj. Gen. Wang Haiyun wrote China should not only intervene in a Korean conflict but demand no US occupation of North Korean territory, though he said he did not speak for the government. He made similar comments in an op-ed in the state-owned Global Times in March, CNN reports.