BEIJING — It was supposed to be Xi Jinping’s moment to bask in global prestige, as the Chinese president hosted the leaders of some of the world’s most dynamic economies at a summit meeting just weeks before a Communist Party leadership conference.
But just hours before Mr. Xi was set to address the carefully choreographed meeting on Sunday, North Korea’s leader, Kim Jong-un, detonated his sixth nuclear bomb.
Mr. Kim has timed his nuclear tests and missile launches with exquisite precision, apparently trying to create maximum embarrassment for China. And on Sunday, a gathering in southeast China of leaders from Russia, Brazil, India and South Africa, members of the so-called BRICS group, was immediately overshadowed by news of the test, which shook dwellings in China and revived fears of nuclear contamination in the country’s northeast region.
This is not the first time Mr. Kim has chosen a provocative moment to flaunt his country’s weapons. In May, he launched a ballistic missile hours before Mr. Xi spoke at a gathering of world leaders in Beijing assembled to discuss China’s signature trillion dollar One Belt, One Road project.
The confluence of North Korea’s nuclear testing and Mr. Xi’s important public appearances is not a coincidence, analysts said. It is intended to show that Mr. Kim, the leader of a small, rogue neighboring state, can diminish Mr. Xi’s power and prestige as president of China, they said. In fact, some analysts contended that the latest test may have been primarily aimed at pressuring Mr. Xi, not President Trump.
China always aims for domestic calm in the period leading up to the secretive congress, and so it is unlikely to do anything before Oct. 19, the start of the conclave, Mr. Zhao said.
The biggest concern for China’s leadership is the possibility of North Korea turning on China, the country’s only ally. “If cornered, North Korea could take military action against China, given the relationship has reached a historic low,” Mr. Zhao said.
China supplies more than 80 percent of the North’s crude oil, and suspending delivery would be the ultimate economic sanction, more far-reaching than those imposed, with China’s support, by the United Nations.
Even The Global Times, the nationalist, state-run newspaper, said several months ago that China should consider cutting off its oil supplies to North Korea if Mr. Kim detonated a sixth nuclear bomb. But with the party congress looming, the paper modified its position Sunday.
“The origin of the North Korean nuclear issue is the sense of uncertainty that is generated by the military actions of the U.S./South Korea military alliance,” the paper said. “China should not be at the front of this sharp and complicated situation.”
There were also some doubts whether severing oil supplies would make much a huge difference to the North Korean regime. “The economic effects will be substantial but not regime crippling,” said Mr. Hayes of the Nautilus Institute, which specializes in the North’s energy needs.
The hardships, he said, would be most felt by ordinary people, with less food getting to market and fewer people able to travel between cities in buses.
The North’s army has oil stockpiles for routine nonwartime use for at least a year, Mr. Hayes said. “They can last for about a month before they run out of fuel in wartime, at best; likely much earlier,” he said.
Another major concern for the Chinese government is the fears of residentsin the northeast of the country about nuclear contamination from North Korea’s test site at Punggye-ri, not far from the Chinese border.
Many residents in Yanji in Jilin Province, which borders the North, said they felt their apartments shake after the test. Some posted photos of stocks of food and drinks shattered on the floors of a grocery store. At first residents believed the cause was an earthquake, they said, and only later in the day heard the news from state-run media that North Korea had detonated a nuclear bomb.
“I was in my study when the earthquake began,” said Sun Xingjie, an assistant professor at Jilin University in Changchun about 350 miles from the North Korean test site. Mr. Sun said he checked with friends on social media, and they determined from the location and the depth of the explosion that it was a nuclear test.
Even though there is no evidence of any contamination from the test reaching China, it is a worry of residents, Mr. Sun said.
“We are at the border region, so we have a sense of fear about leakage from the nuclear test,” he said.