US President Donald Trump has declared that the Democrats have "no idea what they are doing" in a scathing rant on their transgender policy.

Speaking at a White House press conference, Trump stated: "They have no idea what they're doing. That's why they want men playing in women's sports. That's why they want transgender for everybody. Everybody transgender.

"And they just got walloped in an election in a landslide, and they haven't changed. One thing I saw the other day, the certain gentlemen who were very well known politician, Democrat, was fighting like hell that men should be allowed to play in women's sport. They just don't get it."