Live from the Oval Office, it's Kanye West with a jaw-dropping performance.

The rapper didn't rap. But, seated across from US President Donald Trump at the Resolute Desk, the musician delivered a rambling, multi-part monologue on Thursday that touched upon social issues, hydrogen planes, mental health, endorsement deals and politics.

Seizing the spotlight from the typically center-stage president, West dropped the F-word, floated policy proposals - and went in for a hug.

It was a surreal scene even by the standards of a non-conventional White House. The unlikely allies spoke to reporters before a closed-door lunch that had been billed as a forum to discuss policy issues including manufacturing, gangs, prison reform and violence in Chicago, where West grew up. Spectators at the show included Trump's son-in-law and top adviser, Jared Kushner, former NFL star Jim Brown, the attorney for a gang leader serving time in federal prison, and a gaggle of reporters.

During one pause, Trump seemed to acknowledge the oddness of the moment, saying, "That was quite something."

West discussed prison reform and violence in inner-city Chicago. He brought up Larry Hoover, the leader of the Gangster Disciples who is serving a life sentence for murder, claiming: "The reason why they imprisoned him is that he started doing positive for the community. He started showing that he actually had power, he wasn't just one of a monolithic voice, that he could wrap people around."

Taking questions from reporters, the rapper also voiced concern about stop-and-frisk policing. Trump this week called on Chicago to embrace the tactic, which allowed police to detain, question and search civilians without probable cause, though it was deemed unconstitutional in New York City because of its overwhelming impact on minority residents.

Asked about his comments in 2005 that President George W Bush didn't "care about black people" after hurricane Katrina, West said that "We need to care about all people" and that he "was programmed to think in a victimized mentality."

West himself has suggested he might be open to wading into politics, including a run for president in 2020.

Asked if West could be a future presidential candidate, Trump said, "Could very well be." West shot back, "Only after 2024."