Sales of winter products surged at South Korean convenience stores as temperatures fell sharply this month, industry sources said Friday. According to retailers, sales of disposable hand warmers at GS25 convenience stores, operated by GS Retail Co., rose more than elevenfold in the first seven days of this month compared with the previous week. Sales of tights, worn to keep warm, increased by a similar margin. Demand for popular winter snacks and beverages, such as instant fish cakes, baked sweet potatoes and traditional tea, climbed 653 percent, 132 percent and 50.2 percent, respectively, over the period. CU convenience stores, operated by BGF Retail Co., reported a 400 percent increase in sales of disposable hand warmers over the same period. "As cold weather sets in, sales of winter snacks and cold-weather gear are rising sharply," an industry official said.