Twitter informed employees that the company’s office buildings would be temporarily closed immediately.
The announcement comes amid reports that many staff were quitting after new owner Elon Musk called on them to sign up for “long hours at high intensity” or leave.
The message said, “Please continue to comply with company policy by refraining from discussing confidential company information on social media, with the press or elsewhere.”
According to reports this week, Mr Musk told Twitter staff that he had to commit to long hours and “would have to be extremely tough” or quit the company.
In an email to staff, the company’s new owner said workers would have to take the pledge if they wanted to stay, The Washington Post reported.
Those who did not register by Thursday, November 17, would receive a three-month severance package, Mr Musk said.
Earlier this month, the company cut about 50% of its workforce.
Today’s announcement that Twitter had temporarily closed its offices came amid signs that many workers have also quit because they did not accept Mr Musk’s new terms.
Employees tweeted using the hashtag #LoveWhereYouWorked and a greeting emoji to show they were leaving the company
A former Twitter employee who wished to remain anonymous told the BBC: “I think when the dust clears today, there will probably be less than 2,000 people left.”
They added that all of their team members had been fired.
“The manager of this team, his manager, was fired. And then the manager of this manager was fired. The person above was one of the executives fired on the first day. So there is no one left in this chain of command.”
Before Mr Musk took control of Twitter, the company had about 7,500 employees. The company also reportedly employed thousands of contract workers, most of whom were laid off.
Another person said she quit when she was ready to work long hours.
“I didn’t want to work for someone who repeatedly threatened us by email saying that only ‘exceptional tweeps should work here’ when I was already working 60-70 hour weeks,” they said.
The world’s richest person has become Twitter’s chief executive after buying the company last month in a $44bn (£37bn) deal.
In response to a question about concerns that Twitter was about to shut down after the Twitter office shutdown message was sent, Mr Musk tweeted:
“The best stay, so I’m not super worried.”
In a separate post, he said: ‘And…we just hit another Twitter usage record, lol’.