Apple maestro Steve Jobs has taken the stage to a standing ovation to unveil the iPad 2 with a surprise return to the spotlight after a brief medical absence.

The familiar sight of the Silicon Valley legend in a black turtleneck and jeans cheered fans and investors who had fretted about the health of the charismatic company co-founder.

Jobs, who has been treated for a rare form of cancer, had been on indefinite medical leave for an undisclosed condition.

Shares of Apple, which had been flat, climbed as much as 1.4 per cent after he strode onstage.

In the run-up to the event, there had been almost as much speculation about whether Jobs would appear as there was about the device itself.

"Didn't want to miss today," he told a packed auditorium in San Francisco.

Apple is launching the next generation of its ground-breaking tablet computer just as its main adversaries are releasing their first such devices.

The iPad 2 is thinner than the iPhone 4, twice as fast as the last tablet, camera-equipped, and goes on sale this month in a surprisingly fast roll-out that highlights the fierce competition in the tablet market.

Apple sold nearly 15 million iPads in nine months of 2010, two or three times as many as analysts had predicted. The company is expected to sell 30 million or more this year, which would generate close to $20 billion in sales.