Apple's stock fell by nearly 10 per cent on Friday after a report posted on CNN suggested that Steve Jobs had suffered a heart attack.

The story was posted on CNN's iReport site for citizen journalists and caused Apple's stock to dip over nine per cent before the company denied the story.

The US Securities and Exchange Commission is now investigating to see whether the bogus report was an act of deliberate stock manipulation.

"After the content in question was uploaded to iReport the community brought it to our attention," said CNN.

"The fraudulent content was removed from the site and the user's account was disabled."

The report was posted at around 7am by a user known only as 'Johntw'. It claimed that Jobs had been hospitalised after "suffering from severe chest pains and shortness of breath".

After the denial was issued the stock rallied, but ended the day three per cent down.

This is not the first time that questions over Jobs's health have caused concern. After a bout of pancreatic cancer four years ago there have been persistent rumours about the Apple chief's health, something he joked about at his last public appearance.

The rumours were not helped when Bloomberg accidentally published Jobs's obituary in August.