Apple Inc CEO Steve Jobs strode back into the spotlight on Monday to unveil the iCloud, a music-streaming service that the company hopes will power its next stage of growth and popularize Web-based consumer services.

Jobs' decision to appear such events often is news in itself, and appearing on Monday likely will hearten investors worried about his health after the pancreatic cancer survivor went on his third medical leave in January for an undisclosed condition.

A slim-looking Jobs received a standing ovation from the more than 5,000 Apple faithful at its Worldwide Developers' Conference in downtown San Francisco, making a few comments before ceding the stage to marketing chief Phil Schiller.

Apple shares were up 0.3 percent at $344.41 following the latest appearance by Jobs at San Francisco's Moscone center.

The CEO emerged from medical leave to unveil a new Internet-based service for consumers called the iCloud, which lets users play their music and access their data from any Apple device -- a crucial capability for users increasingly accustomed to performing a variety of tasks on the move.

Its expansion into cloud computing -- providing services from the Web -- comes as the company strives to stay a step ahead of rivals such as Google Inc and in the mobile and online content business.

Apple, legendary for keeping its agenda under wraps, has been unusually open about what it plans to show at its annual developers' conference, a five-day extravaganza for developers who rely on Apple for much of their livelihood.

Live Blog of the event:

(Reporting by Poornima Gupta and Noel Randewich. Editing by Robert MacMillan)