Amazon's cloud computing service is likely to face increasing price competition, the analysts said.

"The continued significant investment cycle is not showing any signs of letting up ... ," Raymond James analysts said in a note. The brokerage cut its rating on the stock to "outperform" from "strong buy."

At least 13 analysts cut their price targets on the stock after the company reported the increase in spending that overshadowed better-than-expected quarterly revenue.

Amazon.com's shares dropped more than 9 percent Friday, after analysts raised concerns about the high level of spending on technology, content and new warehouses.

Amazon is spending on a range of projects, including developing its own original shows and video games.

It is also moving more forcefully into hardware, with the debut of its Fire TV video streaming box, and is rumored to be developing a smartphone.

"Amazon is throwing a lot out there to try to drive growth," BofA Merrill Lynch analysts wrote in a note. The brokerage cut its price target on the stock to $420 from $435, citing lower comparable multiples in the sector.

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Amazon shares were down more than 9 percent. The stock was the second-biggest loser on the S&P 500 index.

Amazon, which reported after the close of trading on Thursday, forecast an operating loss of $55 million to $455 million for the second quarter, compared with a profit of $79 million in the same quarter last year.

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Among the 14 brokerage notes seen by Reuters, only Cantor Fitzgerald raised its target price on the stock—by $10 to $425.

Cantor Fitzgerald said that while Amazon's investments were likely to pressure profitability in the near term, they would result in "outsized growth and further market share gains" in the future.