The U.S. government was partially shut down early on Saturday in a fierce dispute over President Donald Trump's demands that Congress assign $5 billion US for a wall along the border with Mexico.

After failing to strike a budget deal on Friday, congressional leaders and the White House pledged to keep talking through the weekend in search of a deal to end the shutdown ahead of the Christmas holiday.

The impasse came after Trump threw a wrench into the works earlier in the week by refusing to agree to a short-term funding deal cut by Democratic and Republican senators because it did not include the $5 billion for his border wall.

The U.S. House of Representatives, where Republicans have a majority until Democrats take over on Jan. 3, then passed a bill that included the $5 billion, but it ran aground in the Senate and the shutdown began at midnight on Friday.

After it became clear the House bill lacked the votes to pass, Senate leaders huddled with Vice-President Mike Pence and other White House officials to try to figure out a path forward.

They failed and lawmakers in both houses of Congress were sent home.

Trump tried to blame Democrats.

"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 about two hours before a midnight deadline to pass a stop-gap spending bill. "The shutdown hopefully will not last long."

OUR GREAT COUNTRY MUST HAVE BORDER SECURITY! <a href="https://t.co/ZGcYygMf3a">pic.twitter.com/ZGcYygMf3a</a> —@realDonaldTrump

Democrats repeatedly reminded Trump, and voters, that he said last week he would be "proud" to shut the government down in order to get wall funding.

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

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

Watch: Trump and Democrats argue over wall

Donald Trump tells Democratic Senate leader Chuck Schumer and Democratic House leader Nancy Pelosi he'd be proud to shut down the government over funding the wall 0:54

About three-quarters of federal government programs are funded through to Sept 30 next year, but the financing for all others — including the departments of Homeland Security, Justice and Agriculture — expired at midnight.

Federal parks will close and more than 400,000 federal "essential" employees in those agencies will work without pay until the dispute is resolved. Another 380,000 will be "furloughed," meaning they are put on temporary leave.

Law enforcement efforts, border patrols, mail delivery and airport operations will keep running.

Impasse

For the shutdown to end, both the House and the Senate will have to approve any deal negotiated between Trump's team and Republican and Democratic leaders.

The shutdown could persist at least until a new Congress convenes on Jan. 3, and Democrats take control of the House from Republicans. That does not necessarily mean, however, that Trump would agree to a compromise.

The shutdown comes at the end of a perilous week for the president, one that saw Defense Secretary James Mattis resign in protest after Trump's sudden decision to pull U.S. troops out of Syria.

The Syria move was widely criticized, even by senior Republicans in Congress. And continued heavy losses in the stock market were in part fueled by the political turmoil.

While Trump made the promise of building a border wall a fixture of his 2016 election campaign, it is not a top-tier priority for most Americans.

According to a Reuters/Ipsos poll in late November, only 31 per cent of those surveyed said improved border security should be one of the top three priorities for Congress.

That suggests Trump is taking a political risk by gambling on a shutdown to press his point at a time when Democrats are gearing up for their 2020 presidential primary and looking for issues with which to seize an advantage.