Apple shares fell as much as 3 per cent in trading today following the resignation of chief executive Steve Jobs yesterday.

The company's shares dropped $6.43, or 1.7 per cent, to $369.75 on the Nasdaq index after earlier declining as low as $365 at the start of trading on Wall Street, knocking between $7 billion and $10billionn off the company's value.

However shares later rallied and were down less than 2 per cent, showing more resilience than when the departure was initially announced late yesterday.

Steve Jobs's decision to step down from Apple also erased as much as $52 billion from the benchmark gauge for US stocks, futures trading showed today.

Mr Jobs (56) passed the reins to his right-hand man Tim Cook yesterday, saying he could no longer fulfil the duties in a stunning announcement that raised fears his health has deteriorated further.

Mr Jobs, who fought and survived a rare form of pancreatic cancer and revolutionised the technology arena with the iPhone and the iPad in the past four years, is deemed the heart and soul of a company that recently briefly became the most valuable in America.

The letter and a separate terse, somewhat cryptic statement from Apple raised more questions than it answered about Jobs' health and the future of the company.

While it's unlikely that his departure as chief executive will derail Apple's ambitious product-launch roadmap in the near term, there are concerns about whether the company would be as creative beyond the next year or so without its founder and visionary at the helm.

"There's so much long-term growth priced into the stock that everyone is kind of afraid what's happens a couple of cycles from now," said Hussein Kanji, a venture capitalist and adviser to technology start-ups who was formerly with Accel Partners.

"Apple has defined great products as a function of Steve Jobs, that's the worry for most investors."

Mr Jobs presided over a 9,020 per cent surge in the stock since July 29th, 1997, the day before the San Francisco Chronicle broke the news that he would be named interim chief executive. Over the same period, the shares grew in value to $348.7 billion from $2.08 billion.

The September contract on the Standard and Poor's 500 Index slumped up to 0.6 per cent after Mr Jobs released his statement. The measure's total market value was $9.34 trillion at the close of regular trading at 4 p.m., data compiled by Bloomberg show. Apple fell 5.1 per cent.

In the company statement, Apple co-lead director Art Levinson on behalf of the board praised Mr Jobs' "extraordinary vision and leadership" and "countless contributions to Apple's success", saying he would continue to serve the company with "unique insights, creativity and inspiration."

However, the statement, which also talked about Mr Cook's outstanding performance, said nothing about Mr Jobs' health.

His battle with pancreatic cancer, which has stretched over several years, has been of deep concern to Apple fans, investors and the company's board. Over the past two years, even board members have confided to friends their concern that Mr Jobs, in his quest for privacy, wasn't being forthcoming with directors about the true condition of his health.

Mr Jobs has been on medical leave since January 17th, with his duties being filled by Mr Cook, who was chief operating officer.

Some industry insiders privately expressed concern Mr Jobs' relinquishing the chief executive position was a clear signal he was too ill to keep up its punishing pace.

The 55-year-old Jobs had briefly emerged from his medical leave in March to unveil the latest version of the iPad and later to attend a dinner hosted by US president Barack Obama for technology leaders in Silicon Valley. But his often-gaunt appearance had sparked questions about how bad his illness is and his ability to continue at Apple.

In each of Mr Jobs' three health-related absences, Mr Cook has taken over the helm. But the 50-year-old Alabama native, a former Compaq executive and an acknowledged master of supply-chain management, remains largely untested in Wall Street's view.

That's partly why, despite Mr Cook being viewed as a safe bet to run Apple's sprawling empire, some still think his boss will be very badly missed.

One Silicon Valley chief executive, who declined to be identified because of the sensitive issues involved, said the tone of Mr Jobs' statement indicated his health might be worse than publicly known. The Apple chieftain has earned a reputation for commanding every aspect of operations - from day-to-day running to broad strategic decisions - suggesting he would not give up the job if he had a choice.

"It's really sad," he said. "No one is looking at this as a business thing, but as a human thing. No one thinks that Steve is just stepping aside because he just doesn't want to be CEO of Apple anymore."

"It feels like another shoe is going to drop."

While Mr Jobs did not give details on the state of his health, oncologists who have not treated the Apple founder said he could be facing several problems tied to his rare form of pancreatic cancer and subsequent liver transplant. They include possible hormone imbalances or a recurrence of cancer that is harder to fight once the body has already been weakened.

His resignation certainly marks the end of an era at Apple.

A college dropout, a Buddhist and a son of adoptive parents, he started Apple Computer with friend Steve Wozniak in the late 1970s.

The company soon introduced the Apple 1 computer. But it was the Apple II that became a huge success and gave Apple its position as a critical player in the then-nascent PC industry, culminating in a 1980 IPO that made Mr Jobs a multimillionaire.

Despite the subsequent success of the Mac, Mr Jobs' relationship with internal management soured, and in 1985 the board removed most of his powers and he left the company, selling all but one share of his Apple holdings.

Apple's fortunes waned after that. However, its purchase of NeXT - the computer company Mr Jobs founded after leaving Apple – in 1997 brought him back into the fold. Later that year, he became interim chief executive and in 2000, the company dropped "interim" from his title.

"Steve Jobs is the most successful CEO in the US of the last 25 years," Google chairman Eric Schmidt said in a statement. "He uniquely combined an artists touch and an engineers vision to build an extraordinary company…one of the greatest American leaders in history."

Apple previously did not have a chairman, but had two independent co-lead directors. In his letter, which was addressed to the Apple board and the Apple community, Mr Jobs said: "I hereby resign as CEO of Apple. I would like to serve, if the board sees fit, as chairman of the board, director and Apple employee."

They did see fit.

Reuters/Bloomberg