Two men ran across the 69-year-old two-lane bridge into China, glancing back at the North Korean side. Hours earlier, three Chinese citizens had been shot and killed by North Korean guards near a similar crossing hundreds of kilometers to the southwest.

The guards have been “more tense” in recent weeks, said a 41-year-old Tumen woman hawking North Korean money and pins. They have held up transit of Chinese traders as tensions between the two Koreas rose following the March 26 sinking of a South Korean warship, said the woman, who gave only her surname, Li, because she said she feared being punished for divulging information to a foreign reporter.

North Korea said May 26 that it would sever most ties with the South following a report by an international panel led by South Korea that concluded a North Korean torpedo sank the ship, killing 46 sailors.

Tumen’s streets were largely devoid of traffic, and a rock band from the provincial capital of Changchun played to only a scattering of onlookers steps from the Li Ning store.

Shopkeepers had a ready explanation: emigration to South Korea by the region’s ethnic Korean population. More than 92 percent, or 1.78 million, live in Jilin, Heilongjiang and Liaoning provinces, with the heaviest concentration in the prefecture encompassing Tumen.

South Korean statistics back up their claim. There were 363,087 ethnic Koreans from China living legally in South Korea last year, compared with 310,485 in 2007, according to the Ministry of Justice.

Salaries in South Korea are one attraction. A 45-year-old taxi driver with the surname Zhang said his wife had obtained a forged marriage certificate showing she was married to a South Korean. She works in a factory there, making air conditioners and earning the equivalent of 10,000 renminbi a month, five times his wages. She saves 80,000 renminbi a year and plans to return to China soon, he said. Mr. Zhang did not want to use his full name because of his wife’s illegal means of obtaining a visa.