Elon Musk has formally completed his $US44 billion ($68 billion) acquisition of Twitter, immediately firing multiple top executives including CEO Parag Agrawal.

Mr Musk had previously accused the company's leadership team of misleading him over the number of spam accounts on the platform.

Reuters reported Mr Musk terminated Mr Agrawal, chief financial officer Ned Segal and legal affairs and policy chief Vijaya Gadde upon the deal's close, citing unnamed sources.

Mr Agrawal and Mr Segal were in Twitter's headquarters when the acquisition closed and they were escorted out, according to Reuters. 

The New York Times and the Washington Post reported Mr Musk also fired general counsel Sean Edgett. 

The departures come just hours before a Friday deadline set by a Delaware judge to finalise the purchase. She threatened to schedule a trial if no agreement was reached.

On Thursday, Mr Musk attempted to soothe leery advertisers — Twitter's chief source of revenue — in a post saying he was buying the company to help humanity and did not want it to become a "free-for-all hellscape". 

"The reason I acquired Twitter is because it is important to the future of civilisation to have a common digital town square, where a wide range of beliefs can be debated in a healthy manner, without resorting to violence," he wrote in an unusually long tweet for the billionaire. 

There had been concerns Mr Musk's plans to promote free speech by cutting back on content moderation would open the floodgates to more online toxicity and drive away users.

But Mr Musk told advertisers Twitter should be "warm and welcoming to all". 

He had recently been signalling the deal was going through. On Wednesday he paid a visit to Twitter's San Francisco headquarters and changed his Twitter profile to "Chief Twit".

Overnight, the New York Stock Exchange notified investors it would suspend trading in shares of Twitter before the opening bell on Friday (local time) in anticipation of the company going private under Mr Musk.