As many as 20 U.S. states have filed a motion to block President Donald Trump's method of funding a border wall by diverting federal funds through a national emergency declaration, the New York state attorney general has said, according to Al Jazeera.

"This wall is unnecessary, and an abuse of power that will take away resources that could be used to help Americans across our nation," New York Attorney General Letitia James said on Twitter on Friday.

The states filed a lawsuit in February after Trump declared a national emergency to help build a border wall that was a signature of his 2016 campaign for president. The motion for a preliminary injunction to block Trump's effort that was filed late on Thursday formalised that request.

Separately on Thursday, Speaker Nancy Pelosi said the House of Representatives will sue to block President Trump's transfer of money to pay for the wall.

"The President's action clearly violates the Appropriations Clause by stealing from appropriated funds, an action that was not authorized by constitutional or statutory authority," Pelosi, the top Democrat in Congress, said in a statement.

She said a congressional legal advisory group voted to authorise the lawsuit.

Trump's order would allow him to spend money on the wall that Congress appropriated for other purposes. Congress declined to fulfil his request for $5.7bn to help build the wall this year.

In a stinging rebuke, the Democratic-controlled House passed legislation to terminate the emergency Trump declared at the U.S.-Mexico border but Trump issued the first veto of his presidency in March to block that measure.

"The House will once again defend our Democracy and our Constitution, this time in the courts," Pelosi said in a statement. "No one is above the law or the Constitution, not even the President."

However, U.S. Attorney General William Barr said the president's emergency declaration was legal.