“The public does not want China to be the only friend of the North Korean government, 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.