Twitter is testing a new feature that undermines the most basic principle of its platform, namely that all tweets are public.

Now, for the first time, non-public tweets can be shared using a new trial feature allowing users to make tweets visible only to select people.

"Some tweets are for everyone and others are just for people you've picked," Twitter said on Tuesday, announcing the new feature, called Circle.

Twitter says its new Circle feature allows you to have semi-private conversations on Twitter and build closer connections with a smaller group of people. Up to 150 users can be added to one Circle.

Until now, all tweets have been public and could be seen by all users. The only exceptions to this so far were direct messages between two users who follow each other and the possibility of making all tweets from an account visible only to those approved by the owner.

Tweets published in a circle can neither be retweeted nor shared, Twitter says. The feature is initially available to a small group of users worldwide.

The new feature comes ahead of anticipated major changes under its would-be future boss. Twitter is currently in the middle of a takeover attempt by tech billionaire Elon Musk, who accuses the service of restricting too much free speech on the platform.

Musk agreed with Twitter's board of directors on a deal worth around US$44bil , but is still dependent on enough shareholders wanting to cede their shares to him. Twitter and Musk want to complete the takeover by the end of the year.

 - dpa