Twitter is considering legal action against Meta over its fast-growing rival app Threads.

Threads, which was launched to millions on Wednesday, is similar to Twitter and has been pitched by Meta bosses as a "friendly" alternative.

Twitter's Elon Musk said "competition is fine, cheating is not" - but Meta denied claims in a legal letter that ex-Twitter staff helped create Threads.

More than 30 million people have signed up for the new app, according to Meta.

That is less than a tenth of the estimated 350 million users on Twitter, according to Statista.

According to an SEC filing from 2013, it took Twitter four years to build the same number of users that Threads gained in a day - though Twitter grew its userbase from scratch, while Threads was able to tap into the pre-existing two billion monthly users Meta says Instagram has.

The look and feel of Threads are similar to those of Twitter, BBC News technology reporter James Clayton noted. He said the news feed and the reposting were "incredibly familiar".