Apple shares suffered their worst decline in years on Wednesday as selling momentum gained steam for the longtime tech star and world’s largest company by value.

Apple stock tumbled 6.43 per cent to close at $538.79, and is now down some 23 per cent from its record high earlier this year above $700.

There has been no single catalyst for Apple losing its lustre, although some analysts say it has lost its edge in innovation, and that its iconic iPhone and iPad are facing tougher competition.

Another factor was a disappointing earnings report in October from Apple, which in recent years has powered past analyst forecasts.

“There are plenty of reasons to say the stock is done,” said Michael James, at Wedbush Securities.

“It’s becoming a show-me story, they’re going to have to meaningfully beat estimates on the next report.”

James said a lack of information from the secretive California giant also has the market nervous: “Chatter, rumours and traders sentiment are all going to move the stock meaningfully without any comments from Apple.”

A report from the research firm IDC underlined those concerns, saying that tablets powered by the Google Android system are gaining on the market-leading iPads.

IDC now expects Android’s worldwide tablet share to increase to 42.7 per cent for 2012 from 39.8 per cent in 2011. Apple’s share is expected to slip to 53.8 per cent from 56.3 per cent in 2011.

Trip Chowdhry at Global Equities Research said the market was also jolted by reports that Apple had shifted production of some iMac computers to the United States.

“Apple quality is phenomenal, but you can’t overnight produce something in a different location and expect the same kind of quality and cost structure, and that is creating anxiety,” Chowdhry said.

Jody Giraldo at EquityStation said some investors are merely locking in gains before the end of the year.

“The stock had a very good run over the year and it seems a lot of people continue to sell to lock in some returns,” he said.