U.S. store closings and cutbacks turned the second quarter into the worst in 30 years for strip mall owners, according to a report by New York City-based real estate research firm Reis.

Consumers flocked to low-cost, warehouse-style grocery centers instead of strip malls, which are usually anchored by grocery or drug stores. Roadside malls saw average vacancies spike 0.5 percent to 8.2 percent, a level unseen since 1995. Vacancies at regional malls rose 0.4 percentage points to 6.3 percent, the highest level since the first quarter of 2002, according to the report.

For the first time since 1980, more space became available to rent at strip malls than was rented out - about 3.2 million square feet more. Part of the available space came in the form of 5.7 million square feet of new development that came on the market during the quarter.

The extra space translated into falling rents at strip malls, down 0.1 percent to an average of $17.60 per square foot.