Submitting to mounting pressure amid growing disruption, President Donald Trump has signed a deal to reopen government agencies for three weeks, backing down from his demand that Congress give him money for his border wall first.

Key points: The arrangement leaves Mr Trump's request for border wall funding for later talks

The arrangement leaves Mr Trump's request for border wall funding for later talks The President has said he would declare a national emergency if he did not eventually reach a deal with Democrats

The President has said he would declare a national emergency if he did not eventually reach a deal with Democrats The move came on the 35th day of the shutdown, and after another missed payday for federal workers

Standing alone in the Rose Garden, Mr Trump said he would back legislation funding shuttered agencies until February 15 and try again to persuade politicians to finance his long-sought wall.

The deal he reached with congressional leaders contains no new money for the wall but ends the longest shutdown in US history.

First the Senate, then the House of Representatives swiftly and unanimously approved the deal. Late on Friday (local time), the President signed it into law.

Mr Trump's retreat came in the 35th day of the partial shutdown as intensifying delays at the nation's airports and another missed payday for hundreds of thousands of federal workers brought new urgency to efforts to resolve the standoff.

The shutdown was ending as Democratic leaders had insisted it must reopen the government agencies first, then talk border security.

"The President thought he could crack Democrats, and he didn't, and I hope it's a lesson for him," Senate Democratic leader Chuck Schumer said.

House Speaker Nancy Pelosi said of her members: "Our unity is our power. And that is what maybe the President underestimated."

House Speaker Nancy Pelosi has repeatedly said she will not approve money for a border wall. ( AP: Evan Vucci )

Mr Trump still made the case for a border wall and maintained he might again shut down the government over it.

"If we don't get a fair deal from Congress, the government will either shut down on February 15, again, or I will use the powers afforded to me under the laws and constitution of the United States to address this emergency," Mr Trump said.

The President insisted the deal did not amount to any "concession" being made.

Loading

The President has said he could declare a national emergency to fund the border wall unilaterally if Congress does not provide the money. Such a move would almost certainly face legal hurdles.

Sorry, this video has expired The US President speaks about potentially declaring a national emergency.

Deal includes backpay for works, new SOTU date

As part of the deal with congressional leaders, a bipartisan committee of House and Senate politicians was being formed to consider border spending as part of the legislative process in the weeks ahead.

"They are willing to put partisanship aside, I think, and put the security of the American people first," Mr Trump said.

He asserted that a "barrier or walls will be an important part of the solution".

The deal includes backpay for some 800,000 federal workers who have gone without paycheques. The Trump administration promises to pay them as soon as possible.

The breakthrough came as LaGuardia Airport in New York and Newark Liberty International Airport in New Jersey both experienced at least 90-minute delays in take-offs because of the shutdown.

The world's busiest airport, Hartsfield-Jackson Atlanta International Airport, was experiencing long security wait times, a warning sign the week before it expects 150,000 out-of-town visitors for the Super Bowl.

As the shutdown continued this last week, airport officials in Utah treated unpaid workers to a free barbecue lunch. ( AP: Rick Bowmer )

A new date for the President to deliver his State of the Union address, postponed during the shutdown, is also expected to be included in the deal.

But it will not be January 29 as once planned, according to a person familiar with the planning but unauthorised to discuss it.

Democrats say money for border wall not guaranteed

As border talks resume, Senate Majority Leader Mitch McConnell said he hoped there would be "good-faith negotiations over the next three weeks to try to resolve our differences".

Senator Schumer said that while Democrats opposed the wall money, they agreed on other ways to secure the border "and that bodes well for coming to an eventual agreement".

In striking the accord, Mr Trump risks backlash from conservatives who pushed him to keep fighting for the wall. Some lashed out on Friday for his having yielded, for now, on his signature campaign promise.

Money for the wall is not at all guaranteed, as Democrats have held united against building a structure as Mr Trump once envisioned, preferring other types of border technology.

Asked about Mr Trump's wall, Ms Pelosi, who has said repeatedly she would not approve money for it, said: "Have I not been clear? No, I have been very clear."

The Senate first rejected a Republican plan on Thursday reopening the government agencies through to September and giving Mr Trump the $US5.7 billion he had demanded for building segments of that wall, a project that he had long promised Mexico would finance.

The 50-47 vote for the measure fell 10 shy of the 60 votes needed to succeed.

Minutes later, senators voted 52-44 for a Democratic alternative that sought to open padlocked agencies through to February 8 with no wall money. That was eight votes short.

But it earned more support than Mr Trump's plan, even though Republicans control the chamber 53-47.

It was aimed at giving bargainers time to seek an accord while getting paycheques to government workers who are either working without pay or being forced to stay home.

Contributing to the pressure on politicians to find a solution was the harsh reality confronting many of the federal workers, who on Friday faced a second two-week payday with no paycheques.

Throughout, the two sides issued mutually exclusive demands that have blocked negotiations from even starting: Mr Trump had refused to reopen Government until Congress gave him the wall money, and congressional Democrats had rejected bargaining until he reopened government.