YANJI CITY, China -- Beds shook and teacups clattered in this town bordering North Korea, less than 100 miles from the site where the North said it detonated a nuclear test that exploded midmorning in the midst of Chinese New Year festivities.
"I'm worried about radiation," said a 26-year-old woman as she served customers in a bookstore here. "My family lives in the mountains close to the border. They felt the bed shake on the day of the test. I have no idea whether it is safe or not, though the government says it is."
At home and abroad, China has long been regarded as North Korea's best friend, but at home that sense of fraternity appears to be souring as ordinary people express anxiety about possible fallout from the test last Tuesday. The fact that North Korea detonated the device on a special Chinese holiday did not sit well, either.
Among Chinese officials, the mood toward the young North Korean leader, Kim Jong-un, has also darkened. The Chinese government is reported by analysts to be wrestling with what to do about a man who, in power for a little more than a year, thumbed his nose at China by ignoring its appeals not to conduct the country's third nuclear test, and who shows no gratitude for China's largess as the main supplier of oil and food.
"The public does not want China to be the only friend of an evil regime, and we're not even recognized by North Korea as a friend," said Jin Qiangyi, director of the Center for North and South Korea Studies at Yanbian University in Yanji City. "For the first time the Chinese government has felt the pressure of public opinion not to be too friendly with North Korea."
With its site near the border, Yanji City has long been a hub of North Korean affairs inside China, and people here have a relatively good understanding of their opaque and recalcitrant neighbor. This is often where desperate defectors from the impoverished police state first seek shelter, where legal and illegal cross-border trade thrives, and where much of the population has roots in North Korea.
That familiarity breeds mixed attitudes. There is tolerance among some toward the regime -- mostly from those who profit financially. But there is also great anger among many ethnic Korean Chinese about the almost incalculable suffering of the people living under the Kim dynasty, which relies on gulags to deal with even the glimmers of dissent and where years of failed economic policies have left many people near the edge of starvation.
The test detonated at Punggye-ri in northeastern North Korea last week was considerably more powerful than its first nuclear test in 2006 and as large as, or larger than, one in 2009, according to Western and Chinese experts. It remained unclear whether the test was fueled by plutonium or uranium; a uranium test would exacerbate tensions, suggesting the North had a new and faster way of building its nuclear fuel stockpile.
But to some Chinese, the technicalities seem irrelevant.
In postings on Weibo, China's equivalent of Twitter, people asked about the possible dangers of radioactive fallout from a nuclear test. Many said they were dissatisfied by assurances from the Ministry of Environmental Protection that it had checked for radiation at various border areas after the blast and announced that the levels were normal.
Those fears come amid growing uncertainties by some Chinese foreign policy experts about the continued close relationship with North Korea. In the aftermath of the test, a prominent Chinese political scientist with a penchant for provocative ideas, Shen Dingli at Fudan University in Shanghai, wrote on the Web site of Foreign Policy, based in Washington, that it was time for China "to cut its losses and cut North Korea loose."
Other experts suggested the test could worsen relations between the North and China and urged China's new leadership to consider taking a tougher stance to curb the North's nuclear weapons program, which appears to be advancing after some early technical difficulties.
Such opinions, coupled with new worries among some ordinary Chinese people, pose a problem for the new Chinese leader, Xi Jinping, according to Mr. Jin, who often goes to Beijing to participate in policy discussions about North Korea.
If China decides to go along with the United States' calls for much more stringent sanctions than exist now, there are fears among China's policy makers that the North's government would collapse, possibly setting the stage for mayhem on the border and a reunification of Korea as an American ally. But if China maintains the status quo, it could face mounting criticism among its own citizens.
If it decided to take a harder stance, China could punish North Korea by curtailing its oil shipments, by far the major source of fuel in the energy-starved North, Mr. Jin said.
The oil is piped from Dandong, southwest of here. China charges North Korea the highest price of any country to which it exports oil, said Peter Hayes, executive director of the Nautilus Institute, a San Francisco-based policy group that specializes in North Korea. Despite the cost, those fuel shipments are considered essential to the government's survival, even as they possibly create resentment in the North against its patron.
Another option for China would be to cut the trade of its own businessmen, many of whom have become disillusioned by the tough deals that North Korea imposes, including demanding that Chinese enterprises in the North build their own roads and supply their own electricity.
Western analysts have acknowledged that United Nations sanctions cannot force real change in North Korea as long as China continues its material support.
The Chinese government had hoped that Mr. Kim would be more progressive than his father and drop the North Korean policy called "military first," which means a heavy financial commitment for the nuclear program and the army despite the nation's dire economic conditions, analysts say. But Mr. Kim has defied Chinese advice that he become an economic reformer, settling instead for small pilot programs to free up commerce that analysts say have not yet accomplished much.
Close to Yanji City there are five border crossings into North Korea.
At two of them, there was no sign of any traffic on Friday or Saturday. The crossing at Quanhe had been closed for Chinese New Year until Friday morning, and was closed again at the weekend for the birthday of Kim Jong-il, the father of the current North Korean leader.
At the crossing at Tumen, Chinese couples strolled along the icy pathway that marks a strip of no-man's land that leads to the barbed wire of the North Korean border. A single Chinese soldier stood at attention.
An elderly gentleman paid 50 cents at a stall for tourists to look through a telescope aimed at the row of plain, low-rise buildings on the other side and gray, snow streaked hills in the distance. Signs in English and Chinese warned visitors about "no photography or shouting at Korea."
Despite the lull in activity, cross-border legal and illegal trade amounts to about $10 billion a year, said Mr. Jin, the policy expert on the North at the university here.
The National Bureau of Statistics estimated that in the overall Chinese economy, the cross-border trade with North Korea was so small it was not a factor, he said. The trade's importance is based, instead, on its contribution to the stability of the North's leadership, which not only relies on Chinese investment, but also often turns a blind eye to unauthorized shipments of food and other goods to help keep its suffering people from considering revolt.
"China's options have reached an impasse," said Mr. Jin. "For now China chooses to maintain the situation in North Korea, not because it wants to prop up an evil regime but because it doesn't see another choice."
Mia Li contributed research.
This article originally appeared in The New York Times.