US Senator Marco Rubio launched his presidential campaign on Monday at a rally in Miami, calling for a new era of American leadership that is not "stuck in the 20th century".

Rubio, son of poor immigrants from Cuba, announced his intention to seek the Republican nomination and presented the 2016 presidential election as "a generational choice" - a clear jab at his more senior rivals, notably the newly-announced Democratic candidate Hillary Clinton and his fellow Republican and potential adversary Jeb Bush.

"I have heard some suggest that I should step aside and wait my turn. But I cannot, because I believe our very identity as an exceptional nation is at stake, and I can make a difference as president," said the conservative 43-year-old first-term lawmaker.