NEW YORK (REUTERS) - Twitter is building a new feature that will allow users to post tweets as long as 10,000 characters, technology news website Re/code reported on Tuesday.

Twitter, which currently has a 140-character limit, may launch the service towards the end of the first quarter but has not set an official date, Re/code reported, citing sources familiar with the plans.

The sources said the character limit could change before the final version of the product is unveiled.

The micro-blogging website, in an attempt to keep the current look for the Twitter timeline, is testing a version of the product which displays 140-character long tweets but expands to reveal more content when users click on the tweet, Re/code said.

Twitter has been experimenting under Jack Dorsey - the company's co-founder who returned as chief executive in October - to make the service more engaging.

In the few months under Dorsey, Twitter introduced the Moments feature, added polls to tweets, rolled out a "buy" button and replaced its star-shaped "favourite" icon with a heart-shaped icon called "like".

Twitter has come under increasing pressure to boost user growth and ad revenue.

It faced its slowest user growth in 2015 - it now boasts just over 300 million users - and was eclipsed by photo-sharing app Instagram, owned by Facebook, which surpassed 400 million users last year.

However, some users took to Twitter to express their opposition to the new feature with the hashtag #beyond140.

"Just say no to #beyond140!" Andrew Wright tweeted.

Re/code reported in September that the new feature was in the works.

Twitter declined to comment.