Mr. Kukharenko was appalled this month by the reaction online to photographs he posted of face masks he had collected for delivery to China. Self-proclaimed Russian patriots assailed him as a “traitor,” who, as one zealous critic said, had forgotten that “China is not an ally but our most important potential opponent and enemy.”

Such views don’t represent mainstream opinion in Blagoveshchensk, but a relationship whose momentum had seemed unstoppable is suddenly stuck. Whether it can start moving again will depend largely on how fast China’s idled economy starts up — and starts consuming the oil and gas that underpin relations between Moscow and Beijing.

Power of Siberia, a new 1,800-mile gas pipeline that opened in December to carry natural gas from Siberia to China, passes under the Amur in Blagoveshchensk. North of the city, Gazprom is building the world’s biggest gas processing plant, largely to serve China.

A more immediate problem, however, is getting the border open again.

Of the more than 200 Chinese students enrolled at the State Pedagogical University in Blagoveshchensk, only a few are now attending class.

Luan Bohan, a 22-year-old Chinese student who stayed in Russia over the Lunar holiday, said he had encountered no overt discrimination. But, he added, children who see him on the street with his face mask sometimes point and shout “Chinese virus, Chinese virus” before running away.

Some residents, though, particularly those who see China as Russia’s best hope of resisting the West, blame the United States for the outbreak.