Apple Inc shares tumbled more than 6% on Wednesday, chalking up their biggest single-day loss in four years as fears grow about intensifying competition in the mobile market.
Moreover, the stock's massive market value meant Apple was almost single-handedly responsible for Wednesday's 1.1% decline in the Nasdaq 100 Index.
Investors and analysts blamed the sell-off on a mix of factors, including a forecast by research firm International Data Corp (IDC) that Apple continues to cede ground to Google Inc's Android gadgets, and unconfirmed reports that at least one major stock-clearing house was raising margin requirements on Apple's stock trades.
Analysts also cited fears about a hike in the capital gains tax in 2013 in the event that ongoing Washington fiscal negotiations fail, as well as news that Nokia had beat Apple to the punch by striking a deal to sell its flagship Lumia through China Mobile, that country's largest wireless carrier.
Wednesday's drop rounded off a bleak 10 weeks for the most valuable US company.
The stock was one of the day's biggest percentage losers on the S&P 500, shedding $35 billion of market value as more than 37 million shares changed hands -- blowing past the company's average daily volume over 50 days of 21 million.
Apple is still up 33% this year, but is down nearly 24% from its record high of $705.07, hit on September 21. The stock slid more than 6.4% on Wednesday to close at $538.8.