Amazon has quietly upgraded its existing Kindle Paperwhite e-readers with double the amount of storage, Digital Spy reported.

The Kindle Paperwhite and its successor Paperwhite 2 previously had 2GB available, but new 2014 models boast 4GB.

E-reading blog The Digital Reader was first to spot the update earlier this week.

Although any upgrades are welcomed, most users will probably not notice the difference given that 2GB was already capable of holding over 1,000 books.

Responding to the report, Amazon said 2014 models of the device should not be considered a Kindle Paperwhite 3.

"This is not a new product - we've added more on-device storage to the existing Kindle Paperwhite," it said.