Amazon has announced its own currency.

For now it's limited to Amazon's app store used with its Kindle tablets.

But there is also speculation the system could extend to other areas of the company's shopping empire.

The online retail giant said that Amazon Coins would be used as an "easy way for Kindle Fire customers to spend money on developers’ apps in the Amazon Appstore".

The currency will be launched in May, with a special promotion giving users of its app store "tens of millions of dollars' worth of free Amazon Coins" to spend on apps.

Developers will make 70% of the sales on every purchase.

6a0148c71fb71b970c017c3697ba65970b800wi

Above: one of Amazon's 'coins'

Amazon said in a statement:

"For customers, it's an easy way to spend money on Kindle Fire apps and games. They'll be able to purchase as they do now, but with the ability to choose to pay with a credit card or using Coins.

For you, it's another opportunity to drive traffic, downloads, and increased monetization. Plus, there's no integration required--you'll get paid the same 70% revenue share whether the customer chooses to use Coins or their own money."