Elon Musk’s tumultuous $US44 billion ($64 billion) bid to buy Twitter is on the verge of collapse, with the Tesla CEO sending a letter to Twitter's board saying he is terminating the acquisition.

However, the social media platform's co-CEO Bret Taylor has responded by saying Twitter will take legal action to ensure the deal goes ahead.

The possible unravelling of the deal is just the latest twist in a saga between the world's richest man and one of the most influential social media platforms.

Much of the drama has played out on Twitter, with Mr Musk — who has more than 95 million followers — lamenting that the company is failing to live up to its potential as a platform for free speech.

Loading

On Friday, shares of Twitter fell 5 per cent to $US36.81, well below the $US54.20 that Mr Musk had offered to pay. Shares of Tesla, meanwhile, climbed 2.5 per cent to $US752.29.

In a letter to the Securities and Exchange Commission, Mr Musk said Twitter had "not complied with its contractual obligations" surrounding the deal, namely giving Mr Musk enough information to "make an independent assessment of the prevalence of fake or spam accounts on Twitter's platform".

Mr Musk's flirtation with buying Twitter appeared to begin in late March.

That was when Twitter said he contacted members of its board, including co-founder Jack Dorsey, and told them he was buying up shares of the company and interested in either joining the board, taking Twitter private or starting a competitor.

Then, on April 4, he revealed in a regulatory filing that he had become the company's largest shareholder after acquiring a 9 per cent stake worth about $US3 billion.

At first, Twitter offered Mr Musk a seat on its board. But six days later, Twitter CEO Parag Agrawal tweeted that Mr Musk would not join the board after all.

His bid to buy the company came together quickly after that. 

Mr Musk had agreed to buy Twitter for $US54.20 per share, inserting a "420" marijuana reference into his offer price.

He sold roughly $US8.5 billion worth of shares in Tesla to help fund the purchase, then strengthened his commitments of more than $US7 billion from a diverse group of investors including Silicon Valley heavy hitters like Oracle co-founder Larry Ellison.

Inside Twitter, Mr Musk's offer was met with confusion and falling morale, especially after Mr Musk publicly criticised one of Twitter's top lawyers involved in content-moderation decisions. 

As Twitter executives prepared for the deal to move forward, the company instituted a hiring freeze, halted discretionary spending and fired two top managers.

The San Francisco company has also been laying off staff, most recently part of its talent acquisition team.

AP