WASHINGTON (AFP, REUTERS) - The US House of Representatives adjourned on Friday (Dec 21) without Congress passing a spending deal, assuring a partial government shutdown at midnight as President Donald Trump and lawmakers remain at odds over border wall funding.

Operations for several key agencies will cease starting at 12.01am on Saturday (1.01pm Singapore time), despite last-ditch talks that continued on Capitol Hill between White House officials and congressional leaders in both parties.

Trump is seeking US$5 billion for construction of a wall on the US border with Mexico. Democrats are staunchly opposed, and the absence of an elusive deal means federal funds for dozens of agencies will lapse at midnight.

It remained unclear how long the shutdown will last. But the optics are bad, as hundreds of thousands of federal employees will be either furloughed or forced to work without pay in the run-up to the Christmas holiday.

Trump said he hopes the partial shutdown would not last long.

"We're going to have a shutdown. There's nothing we can do about that because we need the Democrats to give us their votes," Trump said in a video posted to his Twitter account hours before a midnight deadline to pass a stop-gap budget measure.

"The shutdown hopefully not last long."

The House is due back in session at noon on Saturday (1am Sunday Singapore time). The Senate meanwhile remained open late on Friday, but there were no signs yet of a breakthrough, and the chamber was quiet.

Senators told reporters that congressional leaders from both parties were negotiating behind the scenes with White House officials including Vice-President Mike Pence, Trump's son-in-law Jared Kushner, and incoming chief of staff Mick Mulvaney.

One focus of discussion was the US$1.6 billion in border security funding that was a part of pending Senate legislation, No. 2 Senate Republican John Cornyn told AFP.

But conservatives in the House would likely baulk at that figure.

"There's no agreement," congressman Mark Meadows, chairman of the House Freedom Caucus of ultra-conservatives, told reporters as he made his way from Senate meetings to the House.

"There's a whole lot of numbers being thrown around", but a maximum US$1.6 billion for border security "is not acceptable".

Trump was scheduled to fly to Florida late on Friday for his Christmas break, but the White House said the president postponed the trip and would remain in Washington in an effort to salvage a spending deal.

Before meeting Senate Republicans at the White House, Trump wrote on Twitter that "Democrats now own the shutdown", despite having said last week that he would be "proud" to close the federal government over the issue of border security and "I'll be the one to shut it down".

Congressional funding for large segments of the government expires at midnight (1pm Singapore time), and a shutdown would ensue if Congress, controlled by Trump's fellow Republicans, does not pass legislation to provide money to keep the agencies open.

"It's possible that we'll have a shutdown. I would say the chances are probably very good," Trump said at the White House.

"We're going to get a wall," Trump added.

Senate Democratic Leader Chuck Schumer put the blame for the impending shutdown squarely on Trump.

"President Trump has thrown a temper tantrum and now has us careening towards a 'Trump shutdown' over Christmas," Schumer said on the Senate floor.

"You're not getting the wall today, next week or on January 3rd, when Democrats take control of the House," Schumer added.

A Schumer spokesman said the senator met Pence, Mulvaney and Kushner.

A senior Senate Republican aide said there was hope that Democrats and Republicans could find a "sweet spot" in a temporary spending Bill that would provide more money for border security than was in the Bill the Senate passed earlier this week - but not the US$5 billion for a wall that the House approved.

A wall along the US-Mexican border to combat illegal immigration and drug trafficking was a key Trump campaign promise in the 2016 election, when he said it would be paid for by Mexico, and he sees it as a winning issue for his 2020 re-election campaign. Democrats oppose the wall, calling it unnecessary and ineffective.

Republican Senators Lamar Alexander and Marco Rubio expressed frustration with what they said was a shifting position by the White House. Rubio said that earlier in the week the Republicans went with their funding bill, which included US$1.6 billion for general border security but nothing specifically for a wall, because Pence had told them the White House was open to such a proposal.

"We had a reasonable path and there was every indication from the president that he would sign it," Alexander said.

PROCEDURAL VOTE

Trump had summoned Senate Republicans to the White House on Friday morning to push for his wall funding before they took up procedural votes on whether to consider a bill passed by the House granting US$5 billion for the wall. But afterward he said there was a good chance the bill would not clear the Senate and that a shutdown was likely.

The procedural vote stretched over several hours because many senators left Washington to start their Christmas break, thinking the temporary funding issue was settled on Wednesday, and had to return to the Capitol.

"If the Dems vote no, there will be a shutdown that will last for a very long time," Trump wrote on Twitter.

Earlier in the week the Senate, where Republicans have a 51-49 majority, passed a short-term government funding bill that included no money for the wall. On Friday Senate Majority Leader Mitch McConnell urged his members to vote for a bill that was approved by the House on Thursday to give Trump US$5 billion toward building the wall on the Mexican border.

In a series of early-morning tweets on Friday, Trump called on McConnell to use the "nuclear option" to force a Senate vote on legislation with a simple majority, rather than the standard "supermajority" of 60 votes.

But there was not enough support among Republican senators to do so.

BAD DAY ON WALL STREET

The possibility of a government shutdown fed investor anxieties that contributed to another down day on Friday for US stocks. The Dow Jones Industrial Average fell 1.82 per cent, the S&P 500 lost 2.06 per cent and the Nasdaq Composite dropped 2.99 per cent.

The showdown added to tensions in Washington as lawmakers also grappled with Trump's sudden move to pull troops from Syria, which prompted Defence Secretary Jim Mattis to resign and furthered concerns over the investigation of Russian meddling in the 2016 election that Trump won.

Three-quarters of government programs are fully funded through the end of the federal fiscal year next Sept 30, including those in the Defence Department, Labour Department and Health and Human Services.

But funding for other agencies, including the Department of Homeland Security, the Justice Department and the Agriculture Department, was set to expire at midnight on Friday.

A partial government shutdown could begin with affected agencies limiting staff to those deemed "essential" to public safety. Such critical workers, including US border agents, and nonessential employees would not get paid until the dispute ends. National parks also would close unless the government declares them essential.

More than half of the 1,700 people who work for the executive office of the president would be furloughed.

Trump had planned to leave Washington on Friday for a holiday stay at his Florida resort, but the stand-off made his plans uncertain.