Online retailer Amazon's cloud computing arm could be worth more than $1 billion (£600 million), according to financial analysts. Amazon Web Services (AWS) started by selling computing power and data storage to emerging technology companies, blogs and websites.

Now the unit counts NASA, the US Department of State, Siemens, Pfizer and Nasdaq among its customers.

Amazon doesn't disclose AWS results, but at the end of the second quarter, S3 held more than 449 billion objects, up 71 percent from the end of last year, according to the official AWS blog. Amazon EC2 is the other main part of AWS, which supplies computing power from the cloud. This service was used by 3,674 of the top 500,000 websites in January, up almost 50 percent year over year, according to a survey by cloud computing expert Guy Rosen.

That put Amazon just ahead of Rackspace Hosting as the largest cloud provider, he noted. AWS generated about $500 million in revenue for last year, according to estimates by analysts at J.P. Morgan, UBS and Citigroup.

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