Elon Musk has countersued Twitter, escalating his legal fight against the social media company over his bid to walk away from the $US44 billion (more than $65 billion) purchase.

While the 164-page document was not publicly available, under court rules a redacted version could soon be made public.

Musk's lawsuit was filed on Friday, hours after Chancellor Kathaleen McCormick of the Delaware Court of Chancery ordered a five-day trial, beginning on October 17, to determine if Mr Musk can walk away from the deal.

Twitter did not immediately respond to a request for comment.

Also on Friday, local time, Mr Musk was sued by a Twitter shareholder, who asked the court to order the billionaire to close the deal, find that he breached his fiduciary duty to Twitter shareholders and award damages for losses he caused.

Mr Musk owes a fiduciary duty to Twitter's shareholders because of his 9.6 per cent stake in the company and because the takeover agreement gives him a veto of many of the company's decisions, according to the lawsuit, which seeks class action status.

The lawsuit was filed by Luigi Crispo — who owns 5,500 Twitter shares — in the Court of Chancery, an equity court.

Mr Musk — the world's richest person and chief executive of Tesla Inc. — said on July 8 that he was abandoning the takeover and blamed Twitter for breaching the agreement by misrepresenting the number of fake accounts on its platform.

Twitter sued days later, calling the fake account claims a distraction and saying Mr Musk was bound by the merger contract to close the deal at $US54.20 per share.

The company's shares ended the trading day on Friday at $US41.61, the highest close since Mr Musk abandoned the deal.

Chancellor McCormick fast-tracked the case to trial last week, saying she wanted to limit the potential harm to Twitter caused by uncertainty around the deal.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume.

Watch

Duration: 2 minutes 20 seconds2m 20s

Twitter has blamed the court fight for slumping revenue and causing chaos within the company.

The two sides had basically agreed to an October 17 trial, but were at odds over the limits of discovery, or access to internal documents and other evidence.

Mr Musk accused Twitter this week of dragging its feet in response to his discovery requests, and Twitter accused him of seeking huge amounts of data that are irrelevant to the main issue in the case: whether Mr Musk had violated the deal's contract.

Loading

In her order on Friday, the chief judge appeared to anticipate discovery disputes to come.

"This order does not resolve any specific discovery disputes, including the propriety of any requests for large data sets," said Chancellor McCormick.

Mr Musk also faces a week-long trial in Wilmington, Delaware, beginning October 24.

A Tesla shareholder is seeking to void — as corporate waste and unjust enrichment — the chief executive's record-breaking, $56 billion pay package from the electric vehicle maker.

Reuters