Amazon has stepped up competition against Apple's iTunes Store by launching AutoRip, giving customers free MP3 versions of physical CDs they have already bought.

From Thursday, customers who bought any of the 50,000 AutoRip-eligible CDs from the Amazon Music Store from 1998 onwards will be able to access digital versions immediately through users' accounts on Amazon's Cloud Player.

Albums initially on offer include Pink Floyd's Dark Side of the Moon, Adele's 21 and Thriller by Michael Jackson. Amazon's vice president of worldwide digital music, Steve Boom, told Reuters the first 50,000 AutoRip albums would be the biggest selling, and that the aim is to encourage take-up of its Cloud Player service.

"When we picked those 50,000 titles we focused on having a substantial majority of our physical CD sales covered," he said. "People will be exposed to Cloud Player and our digital music offering, which is a good thing. We want to take this global."

Amazon launched the service after securing licencing deals with EMI, Warner and Sony as well as independent labels.

The online retailer is aiming to increase its 16% share of the digital music market, which Apple's iTunes Store dominates with 64% share, according to NPD Group. Google's nascent Music service accounts for just 5%.

Cloud Player is accessible through Amazon's Kindle Fire device as well as integration on Samsung TVs and DVD players, Roku media player and Sonos hardware, plus iPhone, iPod and iPad apps.

AutoRip will compete with Apple's iTunes Match service, which scans a user's music collection and matches it in the cloud for £21.99 a year, and Google Music's free scan-and-match service.

"Amazon has done a decent job, but Spotify is disrupting iTunes a little bit everyday," Brian Blair, analyst at Wedge Partners, told Bloomberg. "Amazon Cloud Player, Google Play – I've seen no evidence that suggests you're seeing a migration of users away from iTunes to those services."