US President Donald Trump says he has reached a deal to reopen the federal government after a historic month-long shutdown.

It’s understood White House and Congress agreed to temporarily reopen the government for three weeks while negotiations continue on Mr Trump’s border wall on the Mexican border.

“I am very proud to announce today that we have reached a deal to end the shutdown and reopen the federal government,” Mr Trump said from the Rose Garden as the shutdown reached its 34th day.

“As everyone knows I have a very powerful alternative but I’m not going to use it at this time,” Mr Trump said, referring to his power to declare a state of emergency and instruct the military to begin building the wall.

The agreement includes signing a bill that will pass stopgap funding to reopen previously shuttered government departments until February 15.

Democratic leaders Chuck Schumer and Nancy Pelosi refused to give in to Trump’s demands. Photo: Getty

The shutdown, the longest in US history, has seen wide-ranging and damaging ramifications.

More than 800,000 federal government workers were forced to endure weeks without pay while economists downgraded their first quarter GDP outlook.

Mr Trump said his priority was back paying workers who have been furloughed or forced to work for free for the past five weeks.

“I will make sure that all employees receive their back pay very quickly or as soon as possible,” he said on Friday afternoon (local time).

“It will happen fast.”

The deal signals a major backdown from Mr Trump who failed to force Democrats to pass a spending measure which would include $US5.7 billion ($7.9 billion) in funding for his border wall.

Mitch McConnell, the Senate majority leader, pressured President Donald Trump to accept a temporary deal. Photo: Erin Schaff / NYT

Democrats, emboldened since regaining control of the House this month, have refused to give in to the president’s demands.

As recently as Thursday, the president vowed not to reopen the government until his demands were met.

But the shutdown has had disastrous consequences to his approval ratings and to unity within his own party, with Republicans under increasing pressure to reach a deal with Democrats.

The New York Times reports senior Republicans including Senate majority leader, Mitch McConnell of Kentucky, pressured Mr Trump to accept a deal, or at least agree to a temporary ceasefire with Democrats.

As the shutdown entered its fifth week on Friday, New York’s LaGuardia Airport announced it was no longer accepting incoming flights because of a lack of security staff.

In wide-ranging interviews, government employees spoke of not being able to feed their families or meet mortgage repayments, many of them turning to driving Uber to make ends meet.

The average worker has lost $US5,000 ($6,900) in wages during the shutdown.

While the government has reopened for now, lawmakers are nowhere near out of the woods, with Mr Trump threatening to declare a state of emergency if money isn’t committed to his border wall by the February 15 deadline.

“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 the Constitution of the United States to address this emergency,” Mr Trump said on Friday.

Ebony Bowden contributed reporting from New York City.