Amazon.com says its fourth-quarter net income fell 45 per cent, as higher revenue failed to keep pace with increased spending on order fulfilment and digital content.

The online giant said it earned $97 million, or 21 cents per share, in the October-December period. That is down from $177 million, or 38 cents per share, in the same period a year earlier.

Revenue at the world's biggest online retailer grew 22 per cent to $21.27 billion from $17.43 billion.

FactSet says analysts had expected earnings of 28 cents per share on revenue of $22.26 billion.

For the current quarter, Amazon expects revenue of $15 billion to $16.6 billion. Analysts had expected revenue of $16.86 billion dollars.

Nonetheless, Amazon's stock is up 5 per cent in after-hours trading in the heels of the announcement.