Amazon shares could decline in New York trading to reflect its guidance

The warning came as the online store said that earnings over its crucial Christmas period had more than doubled, boosted by overseas sales.

It said that net income for the three months to the end of December was $207m (�104m), up from $98m last year.

Analysts have blamed a rise in company spending and more product discounting for the weak earnings forecast.

Amazon forecast that sales over the next three months would rise between 31% and 38% to between $3.95bn and $4.15bn, better than many analysts had hoped for.

But of that it said a squeeze on its margins would nevertheless hit profits.

Amazon is facing a tough battle for market share as a third-party seller from rival eBay.

Consumer downturn

Fears of a downturn in US consumer spending have gripped investors in consumer goods firms over the past few months.

But Amazon's chief financial officer Tom Szkutak would not comment on how the problems in the US economy may affect the firm.

"Our business is fine," he said.

"What we think going forward is reflected in our guidance."