Republican Donald Trump is projected to take home the most votes in the Massachusetts primary, CNN projected after polls closed in the state at 8 p.m.

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 four states on Super Tuesday, when 12 states were voting. Trump won Alabama, Georgia, Massachusetts and Tennessee, while Clinton won Alabama, Georgia, Tennessee and Virginia.

Opinion polls heading into the voting showed Trump leading in nearly all of the 12 states up for grabs, raising the possibility of a big night that would intensify worries among Republican leaders who fear the billionaire could inflict long-term damage on the party.

Exit polls indicated that Virginia, Vermont and Oklahoma were too close to call for Republicans as balloting ended in those states, networks said. For Democrats, Massachusetts and Oklahoma were too close to call.

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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 U.S. senator from Vermont.

Sanders won his home state of Vermont, one of five states he was hoping to capture on Tuesday. He thanked cheering supporters in his hometown of Burlington, Vermont, and took a shot at 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 Nov. 8 election to succeed Democratic President Barack Obama. Voting stretches from eastern states to Texas and Minnesota, with the first polls closing at 7 p.m. EST (midnight GMT).

Trump has worried many in the Republican establishment with proposals such as building a wall along the U.S. southern border with Mexico, deporting 11 million illegal immigrants and slapping a temporary ban on Muslims entering the country.

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But 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 March 15.

With a string of victories on Tuesday, Trump would expand his strong lead over U.S. Senator Ted Cruz, U.S. 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 and 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 became the Democratic nominee.

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The crossfire between Trump and establishment Republicans threatened to rip the party apart at a time when it will need to generate momentum behind a prospective nominee. That worries some Republican strategists looking ahead to the nominating convention in July.

"If Trump continues winning, disappointed party elites will need to reconcile with supporting 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 blocs of black voters, who have been slow to warm to Sanders.

In addition to his home state of Vermont, Sanders had been aiming for wins in four other states on Tuesday - neighboring Massachusetts, Oklahoma, Minnesota and Colorado.