Amazon Prime customers already get access to Prime Music streaming as part of their £79 annual fee, but now there's another option: Amazon Music Unlimited has launched in the US for $9.99/month.

The new music streaming service offers "tens of millions" of tracks - far more than Amazon Prime Music's two million - and is designed to integrate with the Amazon Echo voice-controlled speaker just launched in the UK. 

The service is currently available only in the US, where Amazon Prime subscribers will get a $2 discount, making it $7.99 a month. This undercuts archrivals Spotify and the recently revamped Apple Music.

Amazon Echo owners will get the new Unlimited service for even less, at just $3.99 a month, although that low-cost option will work only through the Echo speaker and Alexa app.

Subscribers will get playlists, radio-style stations, offline listening and lyrics display, and those paying $7.99 or $9.99 will be able to listen through their web browsers, iOS and Android apps and supported Sonos and Bose speakers - as well as the Amazon Echo. 

Although Spotify is already integrated into the Echo (provided you are a Spotify Premium subscriber), Amazon Music Unlimited will have one key advantage: it has been designed to integrate more fully with Alexa, the Echo’s voice-control assistant.

Users will be able to ask Alexa to play songs by quoting specific lyrics, songs from a specific time or a selection of songs by mood, such as ‘happy’ or ‘sad’. This makes it a more ‘intelligent’ integration of music streaming than the standard Spotify one.

Amazon Prime Music is available only in the US for now, but will arrive in the UK, Germany and Austria before the end of 2016. We will be testing the Amazon Echo wireless speaker soon.

MORE: Read our Amazon Prime Music review

MORE: Sonos speakers to add Amazon voice control