Top Democratic Party leaders Tuesday asked Donald Trump to stop holding the American people hostage, stop manufacturing a crisis and reopen the government, after the US President blamed them for the impasse over his controversial border wall with Mexico.

Only minutes after President Trump gave his first prime-time address from the Oval Office, House of Representatives Speaker Nancy Pelosi and Senate Democratic leader Chuck Schumer took to the airwaves to blame him for the partial government shutdown, which has now stretched to its 18th day, the second-longest ever.

The Republican president wants USD 5.7 billion to build a wall along the US-Mexican border, which would deliver on his signature campaign pledge.

But Democrats - who recently took control of the House of Representatives - are adamantly opposed to giving him the funds.

"Much of what we have heard from President Trump throughout this senseless shutdown has been full of misinformation and even malice. The President has chosen fear," Pelosi said.

"President Trump must stop holding the American people hostage, must stop manufacturing a crisis and must reopen the government," she said.

For weeks, the President and congressional Democrats have been at an impasse over his demand for federal funding to build the border wall.

In his eight-minute address carried live by all the major US television networks, Trump said the federal government remained shut because of the Democrats.

He said of the situation at the border: "This is a humanitarian crisis, a crisis of the heart and a crisis of the soul."

Last year, Congress passed most of its spending bills, but 25 per cent of the federal government's spending has lapsed during the fraught negotiations.

About 800,000 federal workers are not getting paid during the shutdown, which affects the Departments of Homeland Security, Justice, Agriculture, Treasury, State, Interior, Transportation and Commerce as well as agencies like the Food and Drug Administration, Environmental Protection Agency and Internal Revenue Service.

"Separate the shutdown from the arguments over border security," said Schumer. "There is bipartisan legislation -- supported by Democrats and Republicans -- to reopen government while allowing debate over border security to continue."

"Democrats and the President both want stronger border security," he said. "However, we sharply disagree with the President about the most effective way to do it."

Schumer said the American democracy does not work the way President Trump wants.

"We don't govern by temper tantrum. No president should pound the table and demand he gets his way or else the government shuts down, hurting millions of Americans who are treated as leverage," he said.

Last week, the Democratic-controlled House passed bills to reopen the government without funding for the wall, which Pelosi has called "an immorality."

On Tuesday, Pelosi and Schumer urged Trump to sign them to allow reopening of the federal offices.

But expecting Trump to veto them, Senate Majority Leader Mitch McConnell has not brought the House bills up for a vote. The Kentucky Republican said on the Senate floor that the whole fight is over "one-tenth of one percent of federal spending" and pointed to a vote in 2006 in which Democrats supported building physical barriers at the border.

"This is no newfound, principled objection," McConnell said. "It's just political spite."

Yet as the shutdown has dragged on, some Republican senators have split from their party's strategy and announced support for funding the government without money allocated to build the wall.

The majority of the public has opposed the wall and blamed Republicans for the shutdown, CNN quoted opinion polls as saying.

It is unclear how the spending fight will get resolved.

On Tuesday, Trump said, "The only thing that is immoral is the politicians to do nothing and continue to allow more innocent people to be so horribly victimised."

He has considered declaring a national emergency to circumvent Congress and get the military to build the wall -- an action that would surely be challenged in the courts, US media reported.

While there were about 416,000 apprehensions at the US-Mexico border in the first 11 months of 2018, the most since 2014, that was many fewer than in most years of the preceding three decades, according to the Pew Research Center.