Apple's shares swallow biggest loss in 4 years

NEW YORK/SAN FRANCISCO  (REUTERS) - Apple Inc shares tumbled more than 6 per cent on Wednesday, chalking up their biggest single-day loss in four years as fears grow about intensifying competition in the mobile device market.

The sell-off, fuelled by a forecast by an influential research firm that the iPad maker is continuing to cede ground to rival Google Inc Android gadgets, rounded off a bleak 10 weeks for the most valuable United States (US) company.

The stock was one of Wednesday's biggest percentage losers on the S&P 500, shedding US$35 billion (S$43 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's shares, once among the most desirable of portfolio holdings, have headed steadily south since September on growing uncertainty about the company's ability to fend off unprecedented competition. This year saw a surge in sales of Amazon.com Inc's cheaper Kindle Fire and Microsoft Corp's first foray into the tablet market with its Surface.