[Updated] Amazon.com is booming, in more ways than one.

The e-commerce giant just turned in a big second quarter, with net sales rising more than 50 percent to more than $9.9 billion, topping Wall Street’s expectations of $9.4 billion. The company’s earnings per share of 41 cents were down from 45 cents in the same quarter last year, but still well ahead of the consensus expectation of 35 cents.

One reason for the lower profits: The company continues to spend big on growth — adding a net total of 5,300 employees in the second quarter, bringing its total direct workforce to 43,200 people worldwide, not including contractors and temporary workers. That’s up a whopping 53 percent from this time last year, when Amazon employed a mere 28,300 people, according to company data.

As we reported earlier this month, the company is looking for more room to accommodate that growth by leasing additional space near its new South Lake Union headquarters campus.

For the third quarter, ending in September, Amazon says it expects net sales between $10.3 and $11.1 billion, or growth of 36% to 47%. On average that’s ahead of analysts’ advance projections of $9.5 billion to $10.8 billion, according to a Thomson Reuters poll.

The news release makes no mention of Amazon’s reported plans to launch a multi-purpose tablet device in the third-quarter, but that will no doubt be a topic of questions during the company’s conference call with analysts, coming up at 2 p.m. Pacific time.

Amazon said sales growth of Kindle e-readers “accelerated in second quarter 2011 compared to first quarter 2011,” but the company continued its practice of withholding specific numbers.

The AT&T-sponsored Kindle 3G with Special Offers, introduced July 13, has become the bestselling Kindle, the company said.

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