The United States could lose in a war against either China or Russia, defence officials have warned.

A report commissioned by Congress, and compiled by a dozen former top Democratic and Republican officials, suggested the US was facing a "military crisis" and would struggle to conduct more than one war at a time.

The report said: "America's military superiority, the hard-power backbone of its global influence and national security, has eroded to a dangerous degree.

"It might struggle to win, or perhaps lose, a war against China or Russia. The United States is particularly at risk of being overwhelmed should its military be forced to fight on two or more fronts simultaneously."

Congress had tasked the National Defense Strategy Commission with looking at Donald Trump's sweeping National Defense Strategy.

The panel found that authoritarian nations like China and Russia were pursuing buildups aimed at "neutralising US strengths".