Online retail giant Amazon revealed a four-fold leap in profits to US$80 million (£39.1 million) in the three-months to September 30, boosted by strong sales of the final Harry Potter book, which became the fastest selling book of all time.

Sales at the retailer soared 41 per cent to US$3.26 billion (£1.59 billion) in the period, compared with US$2.31 billion (£1.13 billion) the previous year.

Amazon founder and chief executive Jeff Bezos said: “Customers continue to respond to our low prices, our free shipping and the benefits of Amazon Prime. With our ever-increasing selection, customers are now getting this unusual level of service across many different product categories and with depth of selection in each category.”

The group expects sales to come in between US$1.5 billion and US$5.45 billion (£732.6 million and£2.66 million) in the fourth quarter. Full-year sales are forecast to be between US$14.26 billion and£14.61 billion (£6.96 billion and£7.13 billion).