Workers at the Departments of Interior, Energy, Veterans Affairs, Agriculture and Health and Human Services had their employment terminated in a drive that so far has largely - but not exclusively - targeted probationary employees in their first year on the job who have fewer employment protections.
Almost half of the probationary workers at the US Centers for Disease Control and Prevention and others at the National Institutes of Health are being forced out, sources familiar with the job cuts told Reuters.
The US Forest Service is firing about 3400 recent hires, while the National Park Service is terminating about 1000, people familiar with the plans said on Friday.
The tax-collecting Internal Revenue Service is preparing to fire thousands of workers next week, two people familiar with the matter said, a move that could squeeze resources ahead of Americans' April 15 deadline to file income taxes.
The firings are in addition to the roughly 75,000 workers who have taken a buyout that Trump and Musk have offered to get them to leave voluntarily, according to the White House. That equals about three per cent of the 2.3 million-person civilian workforce.
Trump says the federal government is too bloated and too much money is lost to waste and fraud. The federal government has some $US36 ($A57) trillion in debt and ran a $US1.8 ($A2.8) trillion deficit in 2024, and there is bipartisan agreement on the need for reform.
In addition to the job reductions, Trump and Musk have tried to gut civil-service protections for career employees, frozen most US foreign aid and attempted to shutter some government agencies such as the US Agency for International Development and the Consumer Financial Protection Bureau almost entirely.
Critics have questioned the blunt force approach of Musk, the world's richest person, who has amassed extraordinary influence in Trump's presidency.
Other spending cuts have raised concerns that vital services were in danger. A month after wildfires devastated Los Angeles, federal programs have stopped hiring seasonal firefighters and halted removal of fire hazards such as dead wood from forests, according to organisations impacted by the reductions.
US Treasury Secretary Scott Bessent on Friday shrugged off those concerns, comparing Musk's so-called Department of Government Efficiency (DOGE) to a financial audit.
"These are serious people, and they're going from agency to agency, doing an audit, looking for best practices," he told Fox Business Network.
Fired federal workers expressed shock.
"I've done a lot for my country and as a veteran who served his country, I feel like I've been betrayed by my country," said Nick Gioia, who served in the army and worked for the Department of Defense for a total of 17 years. He joined the United States Department of Agriculture's Economic Research Service in December only to be fired late on Thursday.
"I don't feel like this has anything to do with federal workers, I feel like this is just a game," said Gioia, who lives in Elizabethtown, Kentucky, and has a child with epilepsy.
"To sit here and watch people like Mr Musk tweet out how he feels like he's doing a great job, he doesn't realise what he's doing to people's lives."
About 1200 to 2000 workers at the Department of Energy were laid off, including 325 from the National Nuclear Security Administration, which oversees the nuclear stockpile, sources familiar with the matter told Reuters on Friday.
But those layoffs have been "partly rescinded" to retain essential nuclear security workers, one of the sources said. It was unclear how many of the 325 firings were rescinded.
Three federal judges overseeing privacy cases against DOGE heard cases on Friday on whether Musk's team should have access to Treasury Department payment systems and potentially sensitive data at US health, consumer protection and labour agencies.
In one of those, a federal judge in New York extended a temporary restraining order blocking DOGE from accessing Treasury Department systems. That order had been in place since Saturday.
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