Hillary Clinton faces a growing number of challengers in the lead up to the 2016 American election, with a young Florida MP expected to declare he wants to become America’s president.

Marco Rubio, 43, is scheduled to make a “huge announcement” in Miami on Monday evening, with the Miami Herald reporting the the son of Cuban immigrants will launch his campaign.

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While the US Democratic Party has only presented Mrs Clinton, 67, as a candidate, the Republican field remains wide open.

Mr Rubio joins two other Republican first-term senators who are already running: Ted Cruz of Texas, who like Rubio is Cuban-American, and libertarian-leaning Rand Paul from Kentucky.

Hillary Clinton is running for the second time.

While Mrs Clinton has few serious challengers from within her party – Vice President Joe Biden and former Maryland governor Martin O’Malley have expressed interest but little else – several more Republicans are considering jumping into the fray, including Wisconsin Governor Scott Walker and former Texas governor Rick Perry.

Should Jeb Bush, the son and brother of two former presidents, enter the race as expected, his duel against fellow Floridian Rubio could be one of the more compelling narratives of the 2016 campaign.

Mr Rubio, who often casts his personal arc as the embodiment of the “American Dream”, wants to take voters beyond the dynastic Bush-Clinton dynamic that has ruled US politics for much of the last quarter century.

He and his team have telegraphed some of Mr Rubio’s themes for the Monday night event in Miami, notably that he is the candidate for a “new American century”.

Youthful, charismatic, and articulate on several issues, Rubio hopes to transcend the Republican Party’s reputation for difficulty in connecting with young, Hispanic or African-American voters.

I’m running for president. Everyday Americans need a champion, and I want to be that champion. –H https://t.co/w8Hoe1pbtC

— Hillary Clinton (@HillaryClinton) April 12, 2015

– with AAP