Twitter temporarily closed its offices on Friday after telling employees they would be informed by email later in the day whether they were being laid off.
The move follows a week of uncertainty about the company's future under new owner Elon Musk.
The social media company said in an email to staff it would tell them by 9am Pacific time on Friday about staff cuts.
The company said:
Musk, the world's richest person, is looking to cut around 3 700 Twitter staff, or about half the workforce, as he seeks to slash costs and impose a demanding new work ethic, according to internal plans reviewed by Reuters this week.
Twitter did not immediately respond to a request for comment.
Twitter employees vented their frustrations about the layoffs on the social network, using the hashtag #OneTeam.
User Rachel Bonn tweeted: "Last Thursday in the SF (San Francisco) office, really the last day Twitter was Twitter. 8 months pregnant and have a 9-month-old. Just got cut off from laptop access."
Responding to the #OneTeam thread, Twitter's head of safety and integrity Yoel Roth said: "Tweeps: My DMs (direct message routes) are always open to you. Tell me how I can help."
Roth was the most senior executive to message publicly with a tweet of support for staff who are losing their jobs. He also appeared to still have his job. Last week, Musk endorsed Roth, citing his "high integrity" after he was called out over tweets critical of former US President Donald Trump years earlier.
Roth did not respond to a request for comment.
Twitter said in the email that its offices would be temporarily closed and all badge access suspended in order "to help ensure the safety of each employee as well as Twitter systems and customer data."
The company's office in Piccadilly Circus, London, appeared deserted on Friday, with no employees in sight.
The company said employees who were not affected by the layoffs would be notified via their work email addresses. Staff who had been laid off would be notified with next steps to their personal email addresses, the memo said.
Some employees tweeted their access to the company's IT system had been blocked and feared whether that suggested they had been laid off.
A user with the account @SBkcrn, whose profile is described as former senior community manager at Twitter, tweeted:
A class action lawsuit was filed on Thursday against Twitter by its employees, who argued the company was conducting mass layoffs without providing the required 60-day advance notice, in violation of federal and California law.
The lawsuit also asked the San Francisco federal court to issue an order to restrict Twitter from soliciting employees being laid off to sign documents without informing them of the pendency of the case.
Musk has directed Twitter's teams to find up to $1 billion in annual infrastructure cost savings, according to two sources familiar with the matter and an internal Slack message reviewed by Reuters.
He has already cleared out the company's senior ranks, firing its chief executive and top finance and legal executives. Others, including those sitting atop the company's advertising, marketing and human resources divisions, have departed throughout the past week.
Musk's first week as Twitter's owner has been marked by chaos and uncertainty. Two company-wide meetings were scheduled, only to be cancelled hours later. Employees told Reuters they were left to piece together information through media reports, private messaging groups and anonymous forums.
The layoffs, which were long expected, have chilled Twitter's famously open corporate culture that has been lauded by many of its employees.
"If you are in an office or on your way to an office, please return home," Twitter said in the email on Thursday.
Shortly after the email landed in employees' inboxes, hundreds of people flooded the company's Slack channels to say goodbye, two employees said. Someone invited Musk to join the channel, the sources said.