Those who tried signing onto the popular portal saw a message saying the service was unavailable, and the problem appeared to persist for over an hour. Representatives at Amazon did not return calls seeking comment.
Amazon's overseas websites, such as amazon.co.jp, amazon.co.uk, and amazon.de, appeared to be working without any problems.
The cause of the U.S. website's failure was not immediately clear. Representatives at Internet content delivery company Akamai Technologies Inc, which counts Amazon among its customers, were not immediately available for comment. Amazon shares fell $3.63 or 4.3 percent to $80.88 in late trade. Akamai shares were down $1.79 or 4.6 percent to $37.52.