TOKYO — Toyota lost 765.8 billion yen in the January-March quarter, resulting in its first annual loss in six decades and making the fiscal year its worst since its founding in 1937.

Toyota, whose quarterly loss was bigger than General Motors', also warned today that because of the global auto slump its net loss would deepen in the year through March 2010 to 550 billion yen from 436.94 billion yen in the just-ended fiscal year.

President Katsuaki Watanabe said the devastating results were caused by "the significant deterioration in vehicle sales particularly in the U.S. and Europe," the strong yen and the rising cost of raw materials.

It was Toyota's first annual net loss since 1950. The quarterly loss — down from a profit of 316.8 billion yen a year ago — was bigger than the full-year loss because it had some positive quarters earlier in the fiscal year.

Throughout much of last year, Toyota's sales were booming, thanks to its reputation for quality and good mileage, and the popularity of its Camry sedan and Prius hybrid.

It even overtook General Motors last year to become the world's biggest automaker by annual sales.

But Toyota's business has been hit hard by the U.S. financial crisis and credit crunch, which sent ripple effects around the world, causing people to hold off on buying new cars. The red ink for the full year was worse than Toyota's own forecast for a 350 billion yen net loss.