Twitter's chief executive Parag Agrawal was among those fired, along with the chief financial officer, Twitter's top legal and policy executive and the company's general counsel, the New York Times reported.
A few hours later, Musk tweeted, "the bird is freed," a reference to Twitter's logo.
He had also tweeted a video of himself walking into the company's headquarters on Wednesday carrying a porcelain sink, posting: "Entering Twitter HQ — let that sink in!''
The Tesla CEO also changed his Twitter profile to refer to himself as "Chief Twit" and switched his location to Twitter's San Francisco headquarters.
'Twitter has lots of problems with hate speech'
What's next for Twitter and Musk?
On Thursday he shared a message in which he claimed the speculation over his intentions regarding the purchase of the platform had been "wrong" and that he was buying Twitter to "help humanity."
Twitter's stock had edged closer to Elon Musk's $54.20 (€53.72) per share buyout offer for the platform on Wednesday. That was a sign that investors expected the $44 billion deal to proceed ahead of a court deadline at the end of the week.
The Friday deadline to complete the deal was ordered by the Delaware Chancery Court in early October. The ruling followed an epic battle during which Musk signed a deal to acquire Twitter, then tried to withdraw from it. Twitter subsequently sued the Tesla CEO to force him to go through with the deal.
Elon Musk completes takeover of Twitter
If the parties don't meet the deadline, another legal hearing could take place in November.
Many Twitter users have expressed concern over Musk's pledge to protect "freedom of speech" on the platform including mulling the option of reinstating former President Donald Trump who was kicked off Twitter for his connections with the January 6 riots at the Capitol in Washington.
On Friday, Musk said no Twitter bans would be lifted until being reviewed by a "content moderation council with widely diverse viewpoints."
The deal to put the social media platform into the hands of the richest person in the world has also raised concerns.
How are people reacting?
Reactions to Musk's takeover of the microblogging site were coming in from across the globe on Friday morning.
The EU official overseeing internet regulation cautioned the new Twitter boss that the social media giant must play by the bloc's rules in Europe.
"In Europe, the bird will fly by our (EU) rules," EU internal market commissioner Thierry Breton tweeted, in response to Musk saying "the bird is freed" earlier.
Former US President Donald Trump, who was banned from the platform following the January 6, 2021 riot at the US Capitol, said the service was now in "sane hands." However, he added the caveat this his own website Truth Social "looked and worked better."
"It's been a heck of a rollercoaster, that's for sure, and we're certainly happy from a financial perspective that (the deal) has closed," Steve Johnson, Chief Investment Officer at Australia's Forager Funds Management told news agency Reuters.
"I'll be surprised if senior people here stay around. My guess is with the rest of the business (Musk) will be like he is with all his other businesses - he will be ruthless about 'if you have a job here, you are supposed to be producing something that creates value for the company.' And I think the company has needed that for a long time," he added.
Changpeng Zhao, Founder and CEO of Binance, a co-investor in Musk's Twitter deal said that his company was "excited" to be able to help the tech tycoon "realize a new vision for Twitter."
"We aim to play a role in bringing social media and Web3 together in order to broaden the use and adoption of crypto and blockchain technology," Reuters quoted him as saying.
Meanwhile, Twitter Co-founder Biz Stone thanked the three top executives Elon Musk fired for their " collective contribution" to the platform.
"Massive talents, all, and beautiful humans each!," he said in a Tweet.
Steven Beardsley from DW Business says the question is how is Musk going to use Twitter.
"Is it going to become a cesspool for misleading statements or is it going to be something that is accessible to everyone? How is he going to pull that off and take it from being a joke acquisition to something that's actually very serious and important, maybe even useful," he said.