U.S. vehicles sales declined 10.7% in May, the result of a plunge in truck sales that is shifting the competitive landscape in the world's largest automobile market.

General Motors Corp.'s sales fell 27%, to 268,892 vehicles, according to Autodata Corp. That pulled GM's market share down to 19.2%, the lowest level in at least 50 years.

GM, a big seller of trucks, used to control half the U.S. market. Now, it is in a much-closer race for No. 1 in car sales with Toyota Motor Corp. , which sold 257,404 vehicles. Toyota had a market share of 18.4%.

Ford Motor Co. 's F-150 pickup truck has been the No. 1 seller almost every month over the past three decades. But in May, as consumers flocked to fuel-sipping models, two cars from Toyota and two from Honda Motor Co. outsold the F-150, pushing it down to the No. 5 spot in sales.

The move to cars is "breathtaking," Jim Farley, Ford's group vice president of marketing, said in a conference call. "I would say [it's] the most dramatic shift in customer segmentation potentially in two or three decades."