Efforts to bring a quick end to the US government shutdown floundered Wednesday when senators rejected a plan to resolve an acrimonious funding stand-off between President Donald Trump and Democrats in Congress.

With the government out of money after Trump and lawmakers failed to agree on a deal to keep the lights on, many federal departments and agencies have been closed since midnight.

Senate Democrats -- who are demanding extended health care subsidies for low income families -- refused to help the majority Republicans approve a House-passed bill that would have reopened the government for several weeks while negotiations continue. 

Around 750,000 public sector workers are expected to be placed on furlough -- a kind of enforced leave, with pay withheld until they return to work. 

Essential workers such as the military and border agents may be forced to work without pay and some will likely miss pay checks next week.

Shutdowns are a periodic feature of gridlocked Washington, although this is the first since a record 35-day pause in 2019, when Trump was in his first term. They are unpopular because multiple services used by ordinary voters, from national parks to permit applications, become unavailable.

This time, the shutdown comes against a darker backdrop, with Trump racing to enact hard-right policies, including slashing entire government departments.

The White House is threatening to turn many of the furloughs into mass firings.

"A lot of good can come down from shutdowns," Trump told reporters Tuesday. "We can get rid of a lot of things that we didn't want. They'd be Democrat things." 

Democrats -- motivated by grassroots anger over the expiring health care subsidies for low-income families and Trump's dismantling of government agencies -- have been withholding Senate votes to fund the government as leverage to try and force negotiations.

No compromise

Republicans in the House of Representative have already passed a stop-gap funding fix to keep federal functions running through late November while a longer-term plan is thrashed out.

But the 100-member Senate does not have the 60 votes required to send it to Trump's desk, and Democrats say they won't help unless Republicans compromise on their planned spending cuts -- especially in health care.

"It's the job of senators on both sides of the aisle to come together," top Senate Democrat Chuck Schumer told CNN.

"And here's what we hope now -- that the Republicans have seen they don't have the votes."

With no compromise on the table, both plans were expected to fail again. 

Talks that have taken place so far have been unusually bitter, with Trump mocking Schumer and House Minority Leader Hakeem Jeffries on social media.

Senate Republican leaders, who have just one rebel in their own ranks, need eight Democrats to join the majority and rubber-stamp the House-passed bill. 

They got three moderates to cross the aisle in an initial vote Tuesday and were hoping to peel off five more as the shutdown chaos starts to bite. But Wednesday's result went exactly the same way.

Democrats will be acutely aware however that the party trying to force policy changes by holding back votes on government funding has usually failed in the past.

"Chuck Schumer, at the behest of a bunch of liberal far-left activist groups, has walked his Democrat colleagues into a box canyon. There's no way out, folks," Republican Senate Majority Leader John Thune told reporters at the US Capitol. 

Congress is out Thursday for the Jewish Yom Kippur holiday but the Senate returns to work on Friday and may be in session through the weekend. The House is not due back until next week.