Donald Trump on Saturday inched ahead in his quest to become the Republican Party's presidential nominee, winning internal party elections in the states of Missouri, Michigan and Idaho, US media reported.

The former president has now won every state nominating contest heading into next week's "Super Tuesday," when voters in 15 US states choose their preferred candidate for each party.

Trump has gained huge momentum in the race to capture the Republican nomination at the party convention in July and Tuesday is expected to all but secure the result.

He is likely to face President Joe Biden in November elections, pitting the two for the second time since 2020. The voting Saturday in Missouri, Michigan and Idaho were hybrid internal elections with differing rules, in some cases reflecting rifts and tensions despite Trump's formidable sway.

In Missouri, Trump swamped his main opponent, former South Carolina governor Nikki Haley, winning every county caucus in the state, The New York Times reported.

Anyone who expressed an "allegiance to the Missouri Republican Party" could vote in the county caucuses.

In Michigan, around 2,000 party activists voted in a caucus convention, and Trump won all 39 delegates up for grabs, CNN reported.

The limited vote came in the wake of chaos within the state party, including allegations of overspending and mismanagement.

Trump had grabbed 16 Michigan delegates earlier in the week in a limited primary vote.

The former president also handily won Republican caucuses in the western state of Idaho, NBC and ABC projected.

Haley has raced around the country in the run-up to Super Tuesday, trying to make an increasingly hard case against the inevitability of Trump's nomination. (AFP)