Millions vote in make-or- break Super Tuesday II

Five US states are holding primaries for November's presidential election on what has been dubbed Super Tuesday II, giving Democrat and Republican front-runners a chance to cement their leads.

Polls have opened in Ohio and Florida - both deemed key states - as well as in North Carolina, Illinois and Missouri.

Democratic front-runner Hillary Clinton will hope to fend off a challenge from her resurgent rival, Bernie Sanders.

Meanwhile Donald Trump will aim to edge out his Republican rivals in the race.

The New York real estate mogul is the favourite to win his party's nomination but has run into fierce opposition from within the Republican establishment, as well as facing condemnation from the Democrats.

Sanders, a Vermont senator, and Clinton, a former Secretary of State, have accused Trump of encouraging his supporters to beat up protesters, after violence broke out at a planned appearance by Trump in Chicago.

The latest polls showed the Republican frontrunner poised to win the Tuesday contests, although Ohio's Governor John Kasich held a narrow lead in his state in some surveys.

Victories for any of Trump's rivals - Rubio, Kasich, or Senator Ted Cruz of Texas - would give hope to the Republicans fighting to block him.

Florida, Illinois and Ohio are the day's biggest prizes for both parties, as each state offers large delegate hauls.

Among Democrats, if polls prove accurate Clinton will extend her lead over rival Sanders. She is comfortably ahead in Florida, but in Ohio the former secretary of state only held a five-point lead, according to a Quinnipiac University poll out Monday.