Supermarket sales dropped 4.9 percent last month from a year earlier to 1.317 trillion yen, down for the 30th straight month, the Japan Chain Stores Association said Monday.

The year-on-year percentage change is adjusted for a change in the number of stores.

Sales of seasonal items were strong after the Golden Week holidays in early May thanks to warm weather, but overall sales slowed toward the end of the month as the weather became unpredictable, the industry group said.

"Many supermarkets reported that both the number of customer visits and the value of purchases per customer were declining. Consumer reluctance to buy still remains unchanged," an association official said.

Food sales, which accounted for 53.3 percent of overall sales, dropped 1.7 percent to 702.41 billion yen, while clothing sales, which accounted for 17 percent, slipped 9.1 percent to 223.5 billion yen.

Sales of daily commodities such as sundries, medical and cosmetic goods, furniture, and electrical appliances, which made up 20.2 percent of overall sales, fell 6.9 percent to 266.55 billion yen.

Revenues from travel-related business, ticket sales and other services -- 1 percent of overall sales -- rose 0.2 percent to 13.23 billion yen.

The sales data cover 6,628 outlets run by the association's 109 members.