President Donald Trump has fulfilled a campaign pledge by signing an executive order to withdraw from the Trans-Pacific Partnership (TPP).
The 12-nation trade deal was a linchpin of former President Barack Obama's Asia policy.
"Great thing for the American worker what we just did," said Mr Trump as he dumped the pact with a stroke of a pen.
He also cut funding for international groups that provide abortions, and froze hiring of some federal workers.
Mr Trump's executive order on TPP was largely symbolic since the deal has not been ratified by a divided US Congress.
During his presidential campaign, he criticised the accord as a "potential disaster for our country", arguing it harmed US manufacturing.
His action won some plaudits from the left as well as the right.
Democratic Senator Bernie Sanders told the BBC he backed it because trade deals like this have been a "disaster" and cost millions of jobs.
On Monday evening, Mr Trump's pick to be secretary of state, Rex Tillerson, was approved by the Senate Foreign Relations committee, and now requires confirmation from the full Senate.
And the new CIA boss will be Mike Pompeo, following a Senate vote of 66 to 32, in his favour.
What is the TPP?
- The trade deal, which covered 40% of the world's economy, was negotiated in 2015 by nations including the US, Japan, Malaysia, Australia, New Zealand, Canada and Mexico
- TPP's stated aim was to strengthen economic ties and boost growth, including by reducing tariffs
- It included measures to enforce labour and environmental standards, copyrights, patents and other legal protections
- The agreement, backed heavily by US business, was designed to potentially create a new single market likened to the EU
- Critics argued it was a not-so-secret gambit to box in China, which is not part of the agreement
The Trump administration's first weekday began with a flurry of executive orders, which allow the president to bypass Congress by issuing legally binding directions, mostly of limited scope, to federal agencies.
Mr Trump also signed an order blocking foreign aid or federal funding for any nongovernmental organisation that provides abortions abroad.
The so-called Mexico City policy was first established by Republican President Ronald Reagan in 1984.
It is typically rescinded by incoming Democratic presidents, including Barack Obama in 2009, and reinstated by Republican presidents.
Mr Trump also signed an executive action placing a hiring freeze on non-military federal workers.
After meeting business leaders earlier at the White House, Mr Trump pledged to lower corporate taxes to 15% or 20%, from the current 35%, and slash regulations by up to 75% if they keep jobs in the US.
Mr Trump - whose protectionist rhetoric sent the US dollar falling - also met labour leaders later on Monday.
Some of the measures he announced on Monday fulfil "Day One" pledges he made as a candidate in a speech in Gettysburg in October.
But perhaps inevitably, some of the promises he made on that day and at rallies during his campaign have not been kept, although he may get to them in the coming days and weeks.
Some 'Day One' promises not kept
- Begin building a wall along the US-Mexico border
- Brand China a currency-manipulator
- Eliminate gun-free zones in schools and on military bases
- Ask Congress for legislation on "strong" minimum sentencing for illegal re-entry of a criminal
- Terminate each "unconstitutional executive order"
- "Immediately" suspend the admission of Syrian refugees into the US
The Trump administration has planned for a busy few weeks, according to the White House press secretary.
Sean Spicer said the president's nominee for Supreme Court Justice would come within the next couple of weeks.
And in his first proper White House press briefing, he said the US would block China from taking over contested islands in international waters in the South China Sea.
"I think the US is going to make sure that we protect our interests there," he said.
"It's a question of - if those islands are in fact in international waters and not part of China proper, then yeah, we're going to make sure that we defend international territories from being taken over by one country."
Getting down to business - Anthony Zurcher, BBC News North America Reporter
The start of the Trump administration has looked less like a well-planned parade and more like the running of the bulls in Pamplona. But is there order behind this chaos?
The president and his press secretary spent the weekend blasting the press and its coverage of the inauguration - and that rolling feud unsurprisingly dominated headlines.
Behind the scenes, however, Republicans in the executive branch and Congress are getting down to the business of advancing their political agenda.
The president issued executive orders on trade and abortion on Monday. Congressional committees will soon begin hammering out tax and healthcare legislation.
The bumpy start to Mr Trump's presidency has some questioning whether the president is squandering his power, which traditionally is at its height in the first few months of a presidential term.
Power, however, is what you make of it - and the real test of Mr Trump's strength won't be in the tut-tutting of newspaper editorial pages over tweets and ad-libbed speeches, it will be policies enacted and legislation signed.
While it's easy to dismiss Mr Trump's moves as missteps, if conservatives continue to charge through the chaos, they may learn to love their new president's unconventional style.
Meanwhile, Mr Spicer said it was "unquestionable" that Mr Trump's inauguration "was the most watched" ever.
Although Ronald Reagan's was top in terms of television figures, attracting 41.8 million viewers, Mr Spicer pointed out that the 30.6 million who tuned in to see Mr Trump take the oath of office did not include the millions who watched the ceremony online.
His remarks followed Mr Trump's stinging attack at the weekend on media reporting of attendance figures and the weather at his inauguration.