Donald Trump is poised to declare a national emergency in an attempt to fund his US-Mexico border wall without congressional approval.

The White House said the US president would sign a spending bill that would avert a government shutdown, but which only provides $1.375 billion for border barriers or fencing - far from the $5.7 billion Mr Trump wants.

"President Trump will sign the government funding bill, and as he has stated before, he will also take other executive action - including a national emergency," White House spokeswoman Sarah Sanders said.

The prospect of Mr Trump declaring a state of emergency to build his border wall had appeared more likely after he backed down in the shutdown standoff last month without securing funds for the barrier.

The spectre of such action has produced widespread opposition in Congress, but Mr Trump is under pressure to soothe his conservative base and avoid looking like he's surrendered in his wall battle with Congress.