Amazon.com has said Christmas Day was the "biggest ever day for Kindle book downloads," with two of its top four bestselling 2011 titles being self-published ones. 

The online giant announced that US customers purchased "well over 1m Kindle devices per week" throughout December, with Kindle Fire its Amazon.com bestseller, followed by Kindle Touch at number two, and the Kindle at number three. 

The Kindle was also the bestselling product on Amazon's sites in the UK, Germany, France, Spain and Italy over the holiday season.

Darcie Chan's The Mill River Recluse and Chris Culver's The Abbey, both published independently by their authors using Kindle Direct Publishing, were at number one and number four on the US Kindle bestseller list, Amazon.com said.

Gifting of Kindle books was up 175% between Black Friday (25th November) and Christmas Day in comparison to 2010, it added.