BEIJING — He usually went there for neon-orange jars of citron tea with honey, jumbo packets of dried seaweed, and cartons of eggs that seemed to be perpetually on sale, 15 for eight renminbi, or about a dollar.

But this time was different. Li Xin, a retired store owner, showed up at a Beijing branch of Lotte Mart, a South Korean supermarket chain, with a message.

“Get out of China!” Mr. Li, 66, a tall man in a fraying green parka, shouted at the entrance to a Lotte Mart store in central Beijing. “We don’t want traitors!”

A wave of anti-South Korean sentiment has broken out across China after the South’s embrace of an American missile defense system Washington began shipping this week that China says can be used to spy on its territory.