Bernie Sanders trounced Democratic frontrunner Hillary Clinton in Hawaii's presidential caucus to secure a clean sweep of all three election contests on Saturday, US media reported.

NBC News and other major media outlets projected 71 percent support for Sanders in Hawaii, where 25 delegates were in play, against 29 percent for Clinton.

The Vermont senator enjoyed similarly big wins earlier Saturday in the western states of Alaska and Washington.

US networks projected Sanders winning by wide margins in Washington, where 101 delegates were up for grabs and in Alaska, where 16 delegates were at stake.

Despite being winless over the weekend, the former secretary of state has amassed a huge delegate lead and remains the favorite to win her party's presidential nomination.

Republicans held their caucus vote in Hawaii on March 8, when billionaire businessman Donald Trump garnered 42 percent support to defeat US Senator Ted Cruz with 33 percent.