The US government has officially shut down for the second time this year because Congress failed to meet a deadline to vote on a new budget.
Senators struggled with last-minute objections from Republican Rand Paul, but have now passed the bill, which has gone to the House for its vote.
Federal funding for government services expired at midnight (05:00 GMT).
The 600-page plan proposes an increase in spending, by about $300bn (£215bn), on defence and domestic services.
If the plan is passed in the House of Representatives and signed by the president in the next few hours, the shutdown could be rescinded before the US working day begins on Friday.
But it is not clear how the House will vote, and how public services would be affected on Friday if the shutdown were to continue.
Many government agencies close during a shutdown as their future funding is theoretically not secure. Many employees are asked not to come to work and will not be paid – although some will get back pay.
Employees deemed essential – including military personnel and air traffic controllers – are required to work regardless of shutdowns.
Three weeks ago, some people lost three days of work in a shutdown but this time, it is not yet clear which agencies will close.
The federal Office of Personnel Management said employees should “refer to their home agency for guidance on reporting for duty”.
CNN is reporting that if the shutdown is not averted, government agencies will still be able to call their employees in for a half day’s work to make the shutdown go smoothly.
Some Twitter users shared stories of how the uncertainty would affect people.
While the spending bill’s funding for the Pentagon has delighted the national security wing of the party, fiscal conservatives are up in arms about ramifications for the nation’s debt.
In a doom-laden speech, Senator Paul angrily charged his fellow Republicans with fiscal profligacy, accusing his colleagues of “spending us into oblivion”.
“I ran for office because I was very critical of President Obama’s trillion-dollar deficits,” he said.
“Now we have Republicans, hand in hand with Democrats, offering us trillion-dollar deficits.
“I can’t in all good honesty, in all good faith, just look the other way just because my party is now complicit in the deficits.”
This would be “the very definition of hypocrisy”, he added. -BBC