Both main parties blamed each other for the impasse, with the White House accusing Democrats of being 'obstructionist losers'
The US government has shut down after senators failed to reach agreement on a bill to keep its operations funded.
Lawmakers in Washington DC had a midnight deadline to agree to a short-term bill amid an ongoing delay in Republicans and Democrats reaching agreement on a longer-term budget.
However, only 50 of the required 60 senators voted in favour of the bill - with a majority of Democrats and five Republicans voting against.
A government shutdown sees many federal employees sent home (or 'furloughed') while others - including members of the military - may not be paid.
An estimated 850,000 workers, out of a total 3.5 million, could be told to stay home until politicians manage to reach agreement.
The Senate is due to reconvene on Saturday afternoon local time.
The most recent shutdown occurred in 2013 amid a bipartisan dispute over healthcare legislation. The shutdown lasted for 16 days.
In recent months, the two major US parties have been locked in a stalemate over a number of issues, including efforts to secure new protections for young undocumented immigrants known as 'Dreamers'.
Both houses have passed several shorter-term spending bills as efforts continued to reach a bipartisan deal.
Republicans and Democrats were quick to blame each other for the dramatic impasse.
Senate Majority Leader Mitch McConnell said in a statement: “What we just witnessed on the floor was a cynical decision by Senate Democrats to shove aside millions of Americans for the sake of irresponsible political games.
"A government shutdown was one hundred percent avoidable. Completely avoidable. Now it is imminent."
Democratic leader Chuck Schumer blamed Donald Trump, suggesting "there is no one who deserves the blame for the position we find ourselves in more than President Trump".
Mr Schumer had earlier met the US president at the White House. While both men reported progress had been made, they were unable to reach an agreement to avert a shutdown.
Bernie Sanders - the independent Vermont senator aligned with Democrats - described the president's decision to end protections for 'dreamers' as 'Trump's self-made crisis'.
As the midnight deadline loomed, President Trump - who is marking the one-year anniversary of his inauguration today - took to Twitter to blame Democrats for the situation.
Not looking good for our great Military or Safety & Security on the very dangerous Southern Border. Dems want a Shutdown in order to help diminish the great success of the Tax Cuts, and what they are doing for our booming economy.— Donald J. Trump (@realDonaldTrump) January 20, 2018
In an early Saturday morning tweet, he added:
This is the One Year Anniversary of my Presidency and the Democrats wanted to give me a nice present. #DemocratShutdown— Donald J. Trump (@realDonaldTrump) January 20, 2018
Following the Senate vote, White House Press Secretary Sarah Huckabee Sanders accused Democrats of being 'obstructionist losers'.
On Twitter, supporters of the two different parties used the opposing hashtags #DemocratShutdown and #TrumpShutdown in their respective efforts to blame the other side.
Vice President Mike Pence, meanwhile, made a brief stopover at Shannon Airport this morning, and is reported to have told US Air Force members that "we'll get this thing figured out in Washington":
During a refueling stop in Ireland, Vice President Pence visited with some Air Force members in the terminal, many of whom are headed to Kuwait. “We’ll get this thing figured out in Washington,” he told them. “You guys stay focused on your mission.” pic.twitter.com/r0vKmkmwUx— Jenna Johnson (@wpjenna) January 20, 2018