Amazon has agreed to buy the videogame platform Twitch for $970m, bringing it access to a huge audience who watch games being streamed live via the site.

The three-year-old, San Francisco-based Twitch Interactive streams games being played for non-playing viewers to watch, and hosts gaming events.

It allows viewers to chat with the players and others, lending it some of the qualities of social networking websites, and it sells advertising to generate income.

"Broadcasting and watching gameplay is a global phenomenon and Twitch has built a platform that brings together tens of millions of people who watch billions of minutes of games each month," said Jeff Bezos, founder and chief executive of Amazon.com.

Twitch claims 55 million visitors a month to its website, via desktop computers, tablets and smartphones, and more than one million "broadcasters," gamers who stream video of their games over the Internet via Twitch.

It also says that visitors log in long periods on the website, averaging 106 minutes a day per person, putting it in the leagues of streaming video like Netflix.

In July, Twitch had more than 55 million unique visitors who viewed more than 15 billion minutes of content on Twitch produced by more than one million broadcasters, including individual gamers, pro players, publishers, developers, media outlets, conventions and stadium-filling e-sports organisations, Amazon said.

The online retail giant said it would acquire all of the outstanding shares of Twitch for about $970m in cash, with the deal, already approved by Twitch's shareholders, expected to close by the end of the year.

That would support Amazon in its fight to capture a large share of the streaming audience market.

The online retailing giant is already pressing hard to add users of its streaming movie service, hoping to overtake Netflix.

Amazon shares had climbed 0.7% to $334.02 on media reports that the takeover was looming. Shares were up 0.1% in after-market trade following the announcement.