Hillary Clinton and Donald Trump claimed early victories on Super Tuesday, bolstering their race to win party nomination in the November election.
Clinton was projected to win Georgia and Virginia while her rival Bernie Sanders was on course to victory in his home state Vermont, networks said.
Clinton, the former Secretary of State, needs to win a majority of states on Super Tuesday to clinch the nomination for the presidential election to succeed Barack Obama.
The long-term frontrunner suffered a surprise setback in New Hampshire, where she lost to Senator Sanders, after scraping through narrowly in the Iowa primaries. She regained the momentum with a strong win in South Carolina.
Sanders hopes to win at least five of the Super Tuesday states to remain a credible contender for the nomination.
On the Republican side, Trump looked set to continue his strong run in primaries and caucuses, causing worry to the conventional core of the party.
Many in the Republican party believe Trump will be beaten squarely by Clinton at the November 8 election and the party would suffer long-term damage because of his candidacy.
The billionaire real estate developer was projected to win a vast majority of Super Tuesday states while his immediate rival Senator Ted Cruz was tipped to win his home state Texas.
In the run-up to the primary results, Cruz called for a unified voice from the Republican party against Trump.
"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," he said, according to Reuters.
Cruz is the only Republican to win a state contest besides Trump in this campaign. Pressure will mount on other Republican aspirins Senator Marco Rubio, Ohio Governor John Kasich and Ben Carson.
