Front-runners Donald Trump and Hillary Clinton each took big steps Tuesday in Florida toward their parties' presidential nominations, booking easy victories in the state's primaries.
Florida is the most populous and most closely watched of the five states that voted Tuesday.
US television networks declared that Trump had won Florida, which gives all 99 of its delegates to the Republican Party's July nominating convention.
With 78 per cent of the vote counted, the New York billionaire had 45 per cent. US Senator Marco Rubio of Florida, who had staked his lagging campaign's survival on winning his home state, was a distant second at 28 per cent, followed by US Senator Ted Cruz of Texas with 17 per cent and Ohio Governor John Kasich at 7 per cent.
On the Democratic side, Clinton romped to victory with 65 per cent of the vote, compared to 33 per cent for US Senator Bernie Sanders of Vermont.
The other states that voted Tuesday were the Southern state of North Carolina and the Midwestern states of Ohio, Illinois and Missouri. Turnout was reported to be high in Missouri, Ohio and in the Chicago suburbs of Illinois.
Sanders, a self-described Democratic socialist who serves as an independent in the Senate, has exceeded all expectations as his campaign stubbornly trails Clinton by so far relatively small margins in the delegate count for the left-leaning party's nomination.
Sanders scored a surprise victory last week in Michigan and was giving Clinton tight races in early results from Ohio, Illinois and Missouri.
In Ohio, which like Florida gives the Republican winner all its delegates, Kasich, who has been a distance fourth in the national nominating race, was leading Trump in early counting.
A Kasich victory in his own state could keep Trump from reaching the Republican convention with an outright majority to win the nomination, depending on results in the coming weeks.
Trump already scored a victory early Tuesday before vote counting began in the five states. A Republican party official on the Mariana Islands reported that out of 471 votes cast on the US territory in the Pacific Ocean, Trump came out on top with 73 per cent. Cruz finished second with 24 per cent.