Republican Donald Trump and Democrat Hillary Clinton rolled up a series of primary wins on Tuesday, as the two presidential front-runners looked to take command of their party nominating battles on the 2016 campaign's biggest night of voting.
Trump and Clinton each won five states on Super Tuesday, when 12 states were voting. Trump won Alabama, Georgia, Massachusetts, Tennessee and Virginia, while Clinton won Alabama, Arkansas, Georgia, Tennessee and Virginia.
Opinion polls projected Trump leading in nearly all of the 12 states, raising the possibility of a big night that added to the worries of the Republican leaders who fear the billionaire could inflict long-term damage on the party.
Exit polls indicated that Arkansas, Vermont and Oklahoma were too close to call for Republicans as balloting ended, networks said. For Democrats, Massachusetts and Oklahoma were too close to call.
Clinton, the former secretary of state, hoped to win enough states to take a big step toward wrapping up her nomination fight with rival Bernie Sanders, a democratic socialist US senator from Vermont.
Sanders won his home state of Vermont, one of five states he was hoping to capture on Tuesday. He thanked the cheering supporters in his hometown of Burlington, Vermont, and assailed the Republican front-runner.
"We are not going to let the Donald Trumps of the world divide us," Sanders said, adding that he expected to pile up "hundreds" of convention delegates in voting on Tuesday.
Super Tuesday is the biggest single day of state-by-state contests to select party nominees for the 8 November election to succeed Democratic President Barack Obama. Voting stretches from eastern states to Texas and Minnesota.
Trump's proposals like building a wall along the US southern border with Mexico, deporting 11 million illegal immigrants and slapping a temporary ban on Muslims entering the country has worried many in the Republican Party.
While his campaign has confounded many Republican leaders, the New York real estate developer cites his high poll numbers as proof he is not dividing the party, but expanding its ranks. He preached unity as he looked beyond the day's voting to campaign in Ohio, which votes on 15 March.
Trump looks to expand lead
After Tuesday's victories, Trump would expand his strong lead over US Senator Ted Cruz, US Senator Marco Rubio of Florida, Ohio Governor John Kasich and retired neurosurgeon Ben Carson.
Opinion polls showed Cruz could pull out a win in his home state of Texas. Voting with his wife in Houston, Cruz said he hoped Republicans would see a narrower field emerge on Wednesday.
"For any candidate that wakes up tomorrow morning who hasn't won any states ... I think it's time to start thinking about coming together, unifying and presenting a clear choice," said Cruz, the only Republican to win a state contest besides Trump to date.
Even as Trump advances, many Republican Party leaders do not support his positions and believe he would be easily defeated in November by Clinton, if she becomes the Democrat nominee.
The crossfire between Trump and Republican establishment threatens to rip the party apart at a time when it will need to generate momentum behind a prospective nominee. It has left some of the Republican strategists worried looking ahead to the nominating convention in July.
"If Trump continues winning, disappointed party elites will need to reconcile to support the party nominee," said Tim Albrecht, a Republican strategist in Iowa.
On the Democratic side, opinion polls showed Clinton, who has won three of the first four Democratic contests, with a big lead in six southern states that have large blocks of black voters, who have been slow to warm up to Sanders.
In addition to his home state of Vermont, Sanders had been aiming for wins in four other states on Tuesday - neighbouring Massachusetts, Oklahoma, Minnesota and Colorado.