The stock was down $50.68, or 9.9 percent, at $463.32 in late morning trading.
Even with the stock's decline, Apple Inc. is the world's most valuable company, a position it's held for more than a year. But it's now worth just 4 percent more than No. 2 Exxon Mobil Corp.
Late Wednesday, Apple reported October-December earnings that were flat compared with the year before. It predicted sales growth for the current quarter of around 7 percent —far from the 50-percent-plus rate it's often hit in recent years. Analysts believe Apple is unable to fully capitalize on the global smartphone boom with just one new —and very expensive— phone model every year.