Update: Amazon’s stock dipped 12 percent in after-hours trading, according to Yahoo Finance, under concerns that the company could actually see an operating loss in the fourth quarter as a result of its spending.

Amazon saw net sales jump 44 percent in the third quarter, while net income decreased 73 percent as the Seattle e-commerce giant continued to make big investments in Kindle Fire, publishing and streaming video services and shipping centers.

In a regulatory filing Tuesday reporting third-quarter financial results, Amazon said net sales increased 44 percent to $10.88 billion in the third quarter, compared with $7.56 billion in third quarter 2010.

Net income, meanwhile, decreased 73 percent to $63 million in the third quarter, or 14 cents per share, compared with net income of $231 million, or 51 cents per share, in third quarter 2010.

For the fourth quarter, Amazon projected that its operating results could land between a loss of $200 million and a profit of $250 million.

While the latest earnings report did not match the 51 percent growth in revenue from the second quarter, it is further evidence of Amazon’s rapid growth. Meanwhile, Amazon saw a dramatic decline in net income, compared to the second quarter when Amazon’s net income decreased 8 percent to $191 million.

For the third quarter, which ended Sept. 30, Amazon saw its net income fall dramatically.

Amazon has been adding employees, gobbling up other companies and also racking up potential legal costs related to its growth. The company also has been beefing up its Amazon Prime video offerings and expanding its publishing empire. Amazon also recently launched its Kindle Fire tablet to much fanfare.

Much of the focus has been on Amazon’s spending on Kindle Fire and its efforts to beef up its video and publishing content. But Amazon also has been rapidly expanding its e-commerce side, adding customer service employees and distribution centers across the U.S.

Amazon started the year with 52 centers, with plans to add 15 more by the end of the year. In a conference call with industry analysts CFO Tom Szkutak said the company now is on track to add 17 distribution centers by the end of 2011, bringing the total to 69.

Amazon has aggressively priced the red hot Kindle Fire. To compete with Apple’s iPad, Amazon is selling Kindle Fire at $199, which is less than half of the $499 price tag Apple has on the iPad and which is $50 less that it costs to develop each tablet, according to analysts.

“There is the distinct possibility that an aggressive/successful Fire launch could materially negatively impact Amazon’s margins and EPS near-term,” Mark Mahaney of Citigroup said in a note to investors Monday previewing Amazon’s earnings.