President Donald Trump has threatened to declare a “national emergency” imminently to secure the funding to build his Mexico border wall.

Mr Trump made the comments as he also revealed that he planned to contact steel manufacturers to ask them to design a steel barrier for the southern border.

“I may declare a national emergency dependent on what’s going to happen over the next few days,” Mr Trump told reporters as he left the White House for Camp David.

Mr Trump has vowed not to waver in his demand for a wall along the southern border with Mexico, but has now said the barrier could be made of steel instead of concrete as a potential compromise with Democrats who refuse to fund it.

V.P. Mike Pence and group had a productive meeting with the Schumer/Pelosi representatives today. Many details of Border Security were discussed. We are now planning a Steel Barrier rather than concrete. It is both stronger & less obtrusive. Good solution, and made in the U.S.A.

— Donald J. Trump (@realDonaldTrump) January 6, 2019

“The barrier, or the wall, can be of steel instead of concrete, if that helps people. It may be better,” Mr Trump told reporters at the White House.

The stoush came at the start of the third week of a partial government shutdown resulting from the dispute that has left hundreds of thousands of federal workers idled or without pay.

Democrats have declined to approve the $US5.6 billion ($A7.9 billion) that Mr Trump wants to deliver on his campaign promise to build a wall to curb illegal immigration.

Led by new Speaker Nancy Pelosi, Democrats passed a bill in the House of Representatives last week to reopen the government without wall funding, with Ms Pelosi branding the wall “immoral”.

“This is a very important battle to win from the standpoint of safety, number one, [and] defining our country and who we are,” Mr Trump said on Monday morning (AEDT).

Vice President Mike Pence led a second round of talks with congressional aides on Sunday (US time) about the issue, but Mr Trump said he did not expect those talks to produce results, noting that the principals – himself, Ms Pelosi and Senator Chuck Schumer – were the ones who could solve it quickly.

“If we don’t find a solution, it’s going to go on for a long time. There’s not going to be any bend right here,” Mr Trump said.

Donald Trump with Nancy Pelosi and Chuck Schumer in their stormy Oval Office meeting in December. Photo: Getty

Large chunks of the federal government were shut down on December 22 after lawmakers and the President hit an impasse over Mr Trump’s demand that a bill to keep the federal government operational include money to help build a $US23 billion ($32.3 billion) wall along the US border with Mexico.

About 800,000 government workers are either furloughed or working without pay.

“I can relate,” Mr Trump said when asked if he could relate to the pain of federal workers struggling to pay their bills.

“I’m sure that the people that are on the receiving end will make adjustments.”

Not all Republicans agree with Mr Trump’s cat and mouse game in keeping government agencies closed until the border debate is resolved.

“It is not a sign of weakness to try to figure out a middle ground, and I think that both sides need to indicate a willingness to listen and to compromise,” US Senator Susan Collins of Maine said on NBC.

She called the debate over using steel versus concrete “bizarre”.

–with AAP