Starbucks on Wednesday warned of weaker-than-expected earnings for the second quarter and full year as it struggles to reignite U.S. growth in the "weakest economic environment" in its history, sending its shares down 11 percent.

Starbucks

"The wheels have really come off of this train,'' RBC Capital Markets analyst Larry Miller told Reuters, noting his surprise at the warning. "It's amazing how fast business has derailed. If sales are down mid-single digits, that is a rapid erosion."