Google on Wednesday rolled out a music service for smartphones and tablets powered by its free Android software, in a challenge to streaming radio firms such as Pandora and Spotify.

The launch of Google Play All Access came at the kickoff of a packed developers conference, which features a range of improvements to the Internet giant's products, and saw a surprise appearance by chief executive Larry Page.

"We are here because we share a deep sense of optimism about the potential for technology to improve people lives," said Page, taking the stage to applause a day after disclosing he had been diagnosed with partially paralyzed vocal cords.

"Everything I read about Google is us versus some other company or some stupid thing," he continued.

"I don't find that stuff interesting. Being negative is not how we make progress."

Page appeared calm and confident on stage and spent a half-hour fielding questions from some of the 6,000 developers registered for the annual event.

Questions ranged from privacy and self-driving cars to Google Glass Internet-linked eyewear and the need for more women developers at a gathering that skewed heavily male.

Page spoke candidly about his childhood; his belief technology companies should be allies instead of enemies; and his disclosure about his medical condition on Tuesday.

"After I disclosed my voice issue and got so many great emails and such thoughtful advice, I realized that I should have talked about it sooner," Page said.

"I wondered why people worried about keeping medical information private, and the answer is insurance," he continued. "It makes no sense. We should change the rules around insurance so they have to insure people, that's the whole point."

Page capped an hours-long keynote presentation that updated ranks of software developers, along with more than a million people watching on YouTube and at viewing parties, about improvements to maps, Android, Chrome and more.

Google Play All Access combines the Internet giant's music catalog with users' personal collections in a radio station-style subscription service, according to Android engineering director Chris Yerga.

"Anything I am listening to in All Access I can easily turn into a radio station," Yerga said while unveiling the service at the annual Google developers conference in San Francisco.

"It allows you to explore radio without rules."

All Access launched in the United States with a monthly subscription fee of $10 and will roll out to additional countries "soon," according to Yerga.

The California-based firm was offering discounts to those who sign up quickly for the service.

The number of Android smartphones and tablets activated more than doubled to 900 million in the past year, according to Sundar Pichai, senior vice president of Android and Chrome.

"That is an incredible achievement," Pichai said. "We are incredibly humbled by where we have reached, but remember there are more than seven billion people on this planet so we have a long way to go."

More than 48 billion applications have been downloaded to Android devices from the Google Play store and revenue being made by developers of those mini-programs has increased 2.5 times in the past year, according to vice president of Android product management Hugo Barra.

Google's Android mobile operating system grabbed three out of four smartphones sold in the world in the first quarter of 2013, extending its gains over Apple and its iPhone, a survey showed.

Executive Vic Gundotra took the keynote stage to introduce major upgrades to the Google Plus social network that included move lively pages and automated tools that automatically bring out the best in uploaded photos.

Google also unveiled enhancement to its core strength, online search.

"Starting today, we will be anticipating your next questions," Google's Amit Singhal said while describing how the search engine is being revved to the point where it takes on the role of a smart personal assistant.

"You can pretty much ask Google the way you would ask a friend and be able to get answers from your own world."

Google shares leapt to a new all-time high Wednesday, topping $900 for the first time, closing up 3.25 percent at $915.89.