Amazon.com Inc (AMZN.O) reported first-quarter revenue and profit that topped analysts' estimates, driven by sustained growth in online retail sales and its profitable cloud business, sending its shares up more than four per cent in extended trading on Thursday.

The world's biggest online retailer said net income rose to US$724 million, or US$1.48 per share, from US$513 million, or US$1.07 per share, a year earlier. This marks the eighth straight quarter Amazon has posted a net profit.

Analysts on average had expected a profit of US$1.12 per share, according to Thomson Reuters I/B/E/S.

The company's total net sales rose 22.6 per cent to US$35.71 billion in the quarter ended March 31, compared with the average analyst estimate of US$35.30 billion.

Revenue from Amazon Web Services, the company's fast-growing cloud services business, rose 42.7 per cent to US$3.66 billion, matching the average analyst estimate, according to market research firm FactSet StreetAccount.

Amazon's net sales in North America, its biggest market, jumped 23.5 per cent to US$20.99 billion in the latest quarter.

The company said a stronger dollar impacted its overall sales by US$492 million and that the quarter faced tough comparison with the year-ago quarter, when the Feb. 29 leap day gave shoppers an extra 24 hours to spend.