Apple's stock has tumbled in early trading, hurt by a lacklustre first-quarter performance and a cautious second-quarter revenue outlook.
The shares on Tuesday dropped more than seven per cent, hovering slightly above $US511 ($A585).
The iPhone maker initially lost nearly $US40 billion in market value.
On Monday Apple Inc said it sold more iPhones and iPads in the first quarter than in any prior quarter, but investors were expecting even bigger things from the Cupertino, California, company.
Apple also announced a second-quarter revenue forecast of $US43 billion, below Wall Street's $US46.13 billion estimate.
The company's stock has started losing some ground in the past year due to concerns about slowing growth and growing competition.
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