Elon Musk has made a star appearance at Donald Trump's first cabinet meeting, winning praise from the president for his controversial work as cost-cutting czar.

Trump insisted his team was "thrilled" with the extraordinary power given to the tech billionaire, despite reported tensions over his sweeping cuts and his emails to government workers.

"Is anyone unhappy with Elon?" Trump asked his cabinet. "If they are, we'll throw them out of here," he said to laughs and applause.

Trump later ordered more mass cuts in the US government.

Musk's 'tech support'

Wearing a black "Make America Great Again" baseball cap, Musk expressed confidence he could cut the $US6.7 trillion budget by $US1 trillion this year.

That extremely ambitious target would likely entail significant disruption of government programs. 

But without such deep spending cuts, Musk said, "the country will go de facto bankrupt".

The SpaceX and Tesla tycoon at one point said his job was "humble technical support" for Trump's government.

He then opened his overcoat to reveal a black T-shirt saying "Tech Support" in large white letters.

A 'pulse check' email

Some of the cabinet secretaries were taken by surprise over the weekend when federal workers received an email requiring them to list their accomplishments for the week.

It was a demand that Musk said would result in termination if ignored. But some agencies told employees to ignore the directive, prompting days of confusion over whether Musk and Trump could make good on the threat.

Musk, the world's richest person, told the meeting his email was a "pulse check" to find out whether government pay cheques were going to actual workers.

"We think there are a number of people on the government payroll who are dead," he said, without providing evidence.

Musk dismissed US media reports that some cabinet members were frustrated by the emails.

Trump, after suggesting he would "throw out" any cabinet members unhappy with Musk, said: "Some disagree a little bit, but I will tell you for the most part I think everyone's not only happy, they're thrilled."

An order for more axings

Since Trump took office, about 100,000 of the US's 2.3 million government workers have been fired or taken redundancies. Some fired workers, such as those in nuclear weapons programs, were rehired.

The Trump administration has now ordered agencies to make more cuts. They've been told to submit plans for a "significant reduction" in staffing by March 13.

The new order does not specify numbers. But Trump told the cabinet meeting that the Environmental Protection Agency's administrator, Lee Zeldin, was planning to cut 65 per cent of his more than 15,000 employees.

Lay-offs have so far focused on probationary workers, who have few protections, but the next round is expected to target veteran public servants.

Trump and Musk's unprecedented government overhaul has also frozen foreign aid and halted scientific research.

Increased spending under Trump

Thus far, Trump and Musk have failed to slow the rate of spending.

According to analysis by news agency Reuters, the government spent 13 per cent more during Trump's first month in office than during the same time last year.

That's largely due to higher interest payments on the debt, and rising health and retirement costs incurred by an ageing population.

A push for tax cuts

Amid the cost-cutting, Trump is simultaneously pushing Congress to extend tax cuts that were introduced in 2017.

The cuts were the signature legislative accomplishment of Trump's first term, but are set to expire at year's end.

The non-partisan Committee for a Responsible Federal Budget estimates they added $US2.5 trillion to the nation's debt, which is now at $36 trillion. It estimated that extending the tax cuts could cost more than $5 trillion over a decade.

Republicans are reportedly weighing cuts to healthcare and food aid for the poor to help pay for the tax cuts, though specifics have not yet emerged.

"Their priorities have been focused on ripping health care away from kids, mums and others who need it most," Democratic member of Congress Brittany Pettersen said.

"All to fund tax breaks for billionaires like Elon Musk while increasing our national deficit by trillions of dollars."

Trump again said Republicans were "not going to touch" safety net programs like Medicare, Medicaid and Social Security, and would instead root out what Republicans call waste, fraud and abuse.

But without steep cuts to federal programs, Republicans won't be able to meet their savings goals. And without finding the savings, conservative Republicans won't want to vote for the final package.

Republican House Speaker Mike Johnson said Trump's plans for tariffs on imports, as well as a touted $US5 million "gold card" for rich immigrants, "will change the math".

ABC/wires