The US Supreme Court hands President Donald Trump a victory by letting his administration redirect $2.5 billion in money approved by Congress for the Pentagon to help build his promised wall along the US-Mexico border even though lawmakers refused to provide funding.

A US federal judge has blocked the Trump administration's use of $1 billion in funds to construct a wall along the southern border with Mexico, but declined to issue a permanent injunction.

Acting Pentagon chief Patrick Shanahan has authorises $1 billion to build part of the wall sought by Donald Trump along the US-Mexico border, the first funds designated for the project under the president's emergency declaration.

President Donald Trump, facing the prospect within days of the longest US government shutdown in history, was considering declaring a national emergency that would likely escalate a policy dispute with Democrats over his proposed US-Mexico border wall into a court test of presidential power.