Donald Trump has divulged details of a cognitive test he "aced" -- including a five-word memory challenge he said proved he had the "mental stamina" to lead the US.

"Person. Woman. Man Camera. TV," the US president recited as he revealed details of the much-discussed test to Fox TV on Wednesday.

"The last questions are much more difficult," he said in an interview on "Tucker Carlson Tonight", in which he repeatedly questioned the mental capacity of his Democratic rival Joe Biden.

"Like a memory question. It's like, you'll go: Person. Woman. Man. Camera. TV," the president said. "So they say, 'Could you repeat that?' So I said, 'Yeah. It's: Person. Woman. Man. Camera. TV.'"

"Then, ten minutes, 15, 20 minutes later they say, 'Remember that first question... Give us that again."

"And you go: 'Person. Woman. Man. Camera. TV.'"

"And they say 'that's amazing. How did you do that?'"

"I do it because I have, like, a good memory," Trump continued. "Because I'm cognitively there."

In the interview, Trump also called for his Democratic rival Joe Biden -- currently leading Trump in polls ahead of the November presidential election -- to take a similar test, because "something's going on."

"You need physical stamina," he said. "You need mental stamina... we have to be sharp... President Xi is sharp. President Putin is sharp. Erdogan is sharp."

The interview quickly drew ridicule on social media.

"i seriously cannot keep up," tweeted Sarah Cooper, a Trump impersonator who shot to fame with parodies of some of the US leader's greatest hits, including "How to Obamagate" and "How to strong death totals".

Cooper targeted Trump in a previous video "How to cognitive", in which she lampooned a previous interview he gave to Fox, where he professed to have "aced" an unspecified cognitive test.