Twitter sacked half of its 7,500-strong staff on Friday as new owner Elon Musk launched his major overhaul of the troubled company just a week after his blockbuster takeover.

An internal document seen by AFP said "roughly 50 percent" of employees were impacted and would be denied access to company computers and email on an immediate basis.

Workers around the world were shown the door and took to Twitter to vent their frustration or disbelief and say goodbye to one of Silicon Valley's most iconic companies.

"Woke up to the news that my time working at Twitter has come to an end. I am heartbroken. I am in denial," said Michele Austin, Twitter's director of public policy for the United States and Canada.

"Regarding Twitter's reduction in force, unfortunately there is no choice when the company is losing over $4M/day," Musk tweeted Friday evening in his first comment on the subject, 24 hours after the company's initial email notifying employees of forthcoming layoffs.

Ahead of the layoffs, Twitter closed access to its offices worldwide, asking employees to stay at home to await news of their fate through an email.

"It's a pretty inhumane way to treat people. It seems like a mercenary effort, they're trying to save money at all cost," said one dismissed employee who spoke on the condition of anonymity.

The cull is part of Musk's push to find ways to pay for the mammoth $44 billion deal for which he took on billions of dollars in debt and sold $15.5 billion worth of shares in Tesla, his electric car company.

Company sources said that Musk's teams were imposing a furious pace on the remaining employees, bringing in Tesla developers to oversee the work of "Tweeps," the inhouse name for Twitter workers.

Musk, the Tesla and SpaceX chief, is said to owe $1 billion in annual interest alone to pay for a deal he tried to wiggle out from almost as soon as he made it in April.

Musk has been scrambling to find new ways for Twitter to make money after his mammoth buyout, including an idea to charge users $8 a month for verified accounts.

The moves would help overcome the potential loss of advertisers, Twitter's main source of revenue, with many of the world’s top brands putting their ad buys on hold, spooked by Musk's well-known disdain for content controls.

- 'Messed up!-

The mercurial tycoon on Friday complained on Twitter of a "massive drop in revenue" that he blamed on "activist groups" that were pressuring advertisers.

"We did everything we could to appease the activists. Extremely messed up! They're trying to destroy free speech in America," he added.

This appeared to refer to Musk's recent meeting with civil rights groups in which he heard concerns that Twitter would open the floodgates to hate speech a week before midterm election in the United States.

In an effort to soothe nerves, Musk had vowed that Twitter will not become a "free-for-all hellscape," but since taking over the company he also has shared a tweet relaying a conspiracy theory about an assault on the husband of US House Speaker Nancy Pelosi.

"We are witnessing the real time destruction of one of the world's most powerful communication systems. Elon Musk is an erratic billionaire who is dangerously unqualified to run this platform," said Nicole Gill, Executive Director of Accountable Tech.

She was part of a coalition of 60 rights groups calling on Friday for a boycott by advertisers of the Musk-owned platform.

Derrick Johnson, president of the NAACP, a leading civil rights organization, said it would be "immoral, dangerous, and highly destructive to our democracy for any advertiser to fund a platform that fuels hate speech, election denialism and conspiracy theories."

"Until actions are taken to make this a safe space, we call on companies to pause all advertising on Twitter," he added.

Twitter head of safety and integrity Yoel Roth tried to soothe concerns, saying that about 15 percent of his department had been let go in comparison to the 50-percent cuts company-wide.

The site's "core moderation capabilities remain in place," he tweeted.

Though extremely influential with opinion-makers and celebrities, the California company has long struggled to generate profit and has failed to keep pace with Facebook, Instagram and TikTok in gaining new users.

In the sign that matters were not improving, data showed Twitter may have lost more than a million users since Musk took over.

Estimates from Bot Sentinel, a firm that tracks Twitter accounts, suggested that more than 875,000 users deactivated their accounts between October 27 and November 1, while half a million more were suspended.