US President Joe Biden's impending coronation as the 2024 Democratic candidate was interrupted -- slightly -- on Super Tuesday when a little-known businessman claimed victory in American Samoa.

Jason Palmer beat the incumbent and runaway favorite in the tiny Pacific Ocean territory's caucus, securing a majority there even if most Americans are unaware of who he is.

Of the 91 votes cast, Palmer scooped 51, against Biden's 40, the local party said.

"Honored to announce my victory in the American Samoa presidential primary," Palmer said on Facebook.

"Thank you to the incredible community for your support. This win is a testament to the power of our voices. Together, we can rebuild the American Dream and shape a brighter future for all."

Residents of US territories can vote in primaries but are not represented in the Electoral College system that ultimately decides who wins the White House in the general election.

American Samoa has a history with longshot candidates: billionaire Michael Bloomberg scored his only win of the 2020 Democratic primary race there, before his candidacy flamed out.

And with just four delegates awarded from the win on Tuesday, Palmer is a long way from stealing the nomination from Biden (who still added two of American Samoa's delegates to his own tally, in any case).

The loss was a minor blip on the night for Biden, who otherwise swept the 15 states up for grabs on Super Tuesday.

But the 81-year-old has faced more serious pushback from some sections of his party as he marches toward renomination.

In Michigan last week, more than 100,000 people voted "uncommitted" in the state's Democratic primary, part of a protest aimed at punishing Biden for his support of Israel's war in Gaza.