Amazon.com sales jumped 34 per cent in the third quarter and profit topped analysts' estimates as Prime Day sales boosted its retail business and demand remained strong for its popular cloud service for companies.

The company's shares, which closed down 0.05 per cent on Thursday, rose about 6 per cent in after-hours trading following the quarterly earnings statement. They have gained about 30 per cent this year.

Amazon shares jumped in after-hours trading on the news. Credit:Richard Drew

The world's largest online retailer said net income rose to $US256 million, or 52 US cents per share in the quarter ending September 30. Analysts on average were expecting 3 US cents per share, according to Thomson Reuters I/B/E/S.

Amazon forecast fourth quarter operating income to range from $US300 million to $US1.65 billion. Analysts on average were expecting $US1.5 billion, according to data and analytics firm FactSet.