The world's largest online retailer of new products - Amazon - says sales of digital books are soaring, helping boost sales by 41 per cent in the last fiscal quarter.

Amazon.com released its second quarter trading results overnight (Australian time) Thursday, reporting sales of $6.57 billion in the 13 weeks to the end of June - a massive increase on the $4.65 billion in second quarter of 2009. Excluding the $48 million unfavorable impact from year-over-year changes in foreign exchange rates throughout the quarter, Amazon says net sales would have grown 42% compared with second quarter 2009.

Operating income increased 71 per cent to $270 million in the second quarter, compared with $159 million in second quarter 2009.

"We're seeing rapid growth in Kindle, Amazon Web Services, third-party sales, and retail," said Jeff Bezos, founder and CEO of Amazon.com.

"We're also encouraged by what we see in mobile. In the last 12 months, customers around the world have ordered more than $1 billion of products from Amazon using a mobile device.

"The leading mobile commerce device today is the smartphone, but we're excited by the potential of the new category of wireless tablet computers. Over time, tablet computers could become a meaningful additional driver for our business."