China's foreign minister recently likened the U.S. and North Korea to two speeding trains hurtling toward each other, an analogy that would seem to place China in the role of helpless bystander. And indeed, while tensions have risen, Beijing has been frustrated by its declining influence over the Korean Peninsula.
China "has a grandstand seat but no control," said University of Virginia China scholar Brantly Womack.
The U.S. is piling the pressure on Beijing to use its clout with North Korea to rein in its nuclear and missile programs. China is the North's most important trading partner and ally, but Pyongyang has ignored Beijing's calls for a suspension of those programs and its requests for high-level bilateral talks. China's relations with South Korea, meanwhile, have plummeted over Beijing's vociferous objections to the deployment of a sophisticated anti-missile shield.
"China's approach to the peninsula is under the same strains that it's been under before. The difference is that, this time, the Americans appear to be applying more overt, real pressure," said Dean Cheng, senior research fellow at the Heritage Foundation in Washington, D.C.
A slew of recent missile launches and North Korea's expected test of a sixth nuclear device have heightened concerns that the country is drawing closer to being capable of striking the U.S. with a nuclear weapon — something sure to bring the crisis to a head.
Also complicating matters: The unpredictability of President Donald Trump, who earlier this month tweeted that the U.S. welcomed China's help in resolving the crisis, then added, "If not, we will solve the problem without them!"
Uncertainties also reside in South Korea's election next month to replace disgraced former President Park Geun-hye; her successor is likely to be more conciliatory toward the North. Meanwhile, China continues to insist that it won't stand idly by while Seoul deploys the missile system, known as THAAD, driving home its point by halting package tours to the South and retaliating against a supermarket chain and other South Korean business interests within China.
While THAAD appears to be a done deal, China is playing a long game of reminding South Korea that, as a smaller and weaker nation, it needs to subordinate its security interests to those of China, said Cheng.
"South Korea has been put on notice that future defense efforts will likely also incur costs," Cheng said.
Such criticisms have been reinforced by state media, with the Communist Party newspaper Global Times writing Wednesday that South Korea was also responsible for "fanning the flames" of tensions on the Korean Peninsula by deploying THAAD and failing to encourage Washington to enter into talks.
Beijing is also dealing with divided public opinion domestically. Younger Chinese with only a passing knowledge of the 1950-53 Korean War, in which hundreds of thousands of Chinese troops died fighting alongside their North Korean allies, are increasingly cynical about the traditional friendship between the two countries.
Criticisms of North Korea that were once quickly scrubbed from the internet are now being allowed to circulate, including a scathing speech by historian Shen Zhihua in which he accused Pyongyang of directly working against China's interests.
Analysts say critics may even include Chinese President Xi Jinping, who is said to be deeply frustrated with North Korean leader Kim Jong Un's intransigence since taking power in 2011 following the death of his father, Kim Jong Il.
In the years since, Xi and Kim have never met. Liu Yunshan, a member of the ruling Communist Party's Politburo Standing Committee, is the last important Chinese official to visit North Korea. He attended a military parade and mass rally marking the 70th anniversary of the founding of the Worker's Party of Korea in October 2015, in what appears to have been a one-off attempt to get relations back on track.
Other affronts to Beijing include Kim's execution of his uncle Jang Song Thaek, who had been the regime's main point of contact with China, and the killing earlier this year in Malaysia of Kim's half brother Kim Jong Nam, who was said to live partly under Chinese protection in the gambling enclave of Macau. Malaysia is seeking four North Korean suspects.
While it has less reason to fear a North Korean nuclear weapon, China intensely dislikes instability in its neighborhood and worries about South Korea and Japan responding by going nuclear themselves.
So while it opposes actions that might topple Kim's regime and possibly send a wave of refugees across the Chinese border, China has agreed to successive rounds of sanctions since 2006. In February, it suspended imports of coal from North Korea, depriving the country of an important source of foreign currency.
The U.S. wants Beijing to do more, possibly including cutting off fuel supplies. Trump has floated the idea of offering advantageous trade terms in exchange for help in although no details have been released.
"I think Beijing is prepared to tighten the screws — but only so much. There's no question that Xi Jinping strongly dislikes, even probably detests, Kim Jong Un and wants to resolve this issue," said Paul Haenle, director of the Carnegie-Tsinghua Center at Tsinghua University in Beijing.
However, the range of China's action remains limited by its priorities on North Korea: "No war, no instability, no nukes," in declining order of importance, said Haenle. "The Chinese are never going to go as far as we would like in terms of putting pressure on the regime in Pyongyang."
China has repeatedly called for dialogue between Washington and Pyongyang, either bilaterally or through the six-party process that's been on ice since 2009. China has also urged, to little response, that North Korea suspend its nuclear weapons and missile programs in return for the U.S. and South Korea halting annual wargames that the North considers a prelude to an invasion.
"China's sanctions and persuasion have been so far not very effective, but China is still making its best efforts," said Lu Chao, director of the Border Study Institute of the Liaoning Academy of Social Sciences, a government think tank.
Lu said China is still hopeful a negotiated settlement can be obtained if the U.S. reaches out to North Korea and the international community convinces Pyongyang that no one is planning to attack it or seek regime change.
"As U.S. officials have pointed out, the U.S. is not seeking the collapse of the North Korean regime. That's a very positive expression."