Donald Trump and Hillary Clinton have claimed a series of big primary wins as the two presidential front-runners look to take command of their party nominating battles on the 2016 campaign's biggest night of voting.
On the Republican side, Ted Cruz, a U-S senator from Texas, won his home state and neighbouring Oklahoma, stopping Mr Trump's winning streak and giving hope to Republicans looking for a way to stop the controversial billionaire's potential rise to the nomination.
"We are blessed with a deep, talented, honourable field. For candidates who have not yet won a state, who have not yet racked up significant delegates I ask you to prayerfully consider our coming together, uniting."
But he was no match for Republican frontrunner Donald Trump who recorded several victories saying he was looking forward to a general election fight against Hillary Clinton.
Mr Trump, speaking in Florida, took the opportunity to question Ms Clinton's track record as a politician.
"And, you know, I watched Hillary's (Clinton, Democratic frontrunner) speech and she's talking about 'wages have been poor, and everything's poor, and everything's doing badly, but we're going to make it...' She's been there for so long. I mean, if she hasn't straightened it out by now, she's not going to straighten it out in the next four years, it's just going to become worse and worse. She wants to 'make America whole again' and I'm trying to figure out what is that all about. 'Make America Great Again' (Trump's slogan) is going to be much better than 'making America whole again'."
For the Democrats, Ms Clinton, the former secretary of state, says the stakes have never been higher.
She turned her attention during her victory rally towards her possible Republican opponents.
Ms Clinton criticised what she called the angry, divisive rhetoric from the Republican side.
"Now it might be unusual, as I've said before, for a presidential candidate to say this, but I'm going to keep saying it. I believe what we need in America today is more love and kindness. Because, you know what? You know what? It works. Instead of building walls, we're going to break down barriers and build, build ladders of opportunity and empowerment so every American can live up to his or her potential, because then and only then can America live up to its full potential too."
Ms Clinton's main challenger for the Democratic nomination, Bernie Sanders, won his home state of Vermont, one of five states he was hoping to capture.
Speaking in Vermont after polling, he thanked his supporters.
"You know, I've been all over this country, but the truth is, it is great and great to come home, see all my friends. You know, we want to win in every part of the country, that goes without saying, but it does say something and means so much to me that the people who know me best, the people who knew me as mayor, knew me as congressman and know me as senator, have voted so strongly to put us in the White House, thank you so much!"
Super Tuesday is the biggest single day of state-by-state contests to select party nominees for the November 8 election to succeed Democratic President Barack Obama.
Voting stretches from eastern states to Texas and Minnesota.
