Visitors to the popular e-tail site either could not reach Amazon's home page or received a note from the company.
"There was an internal error in our system," read a message posted on the front door of the site. "We logged the problem and will investigate it later. Our apologies for the inconvenience."
Company representatives did not immediately respond to calls.
The downtime comes as Amazon prepares to announce its quarterly results later today.
Yesterday, the Seattle-based company announced that Joe Galli, its president and chief operating officer, had resigned to become chief executive of VerticalNet.