Hillary Clinton and Donald Trump are the Super Tuesday big winners
Democrat Hillary Clinton won at least six states and Donald Trump at least five in Super Tuesday elections, the biggest day of the primary campaign.
But Ted Cruz ended Mr Trump's winning streak with victories in his home state of Texas and neighbouring Oklahoma.
Democrat Bernie Sanders also won his home state of Vermont and Oklahoma.
Mrs Clinton and Mr Trump were pressing for sweeping victories that could distance them from their party rivals and move them closer to a November presidential election showdown.
Nominating contests were being held in 12 of the 50 US states.
Mr Trump won in Virginia, Alabama, Massachusetts, Tennessee and Georgia. Mr Cruz is the only candidate to have beaten him, in the lead-off Iowa caucuses, as well as the two wins on Super Tuesday.
Mr Cruz, a firebrand conservative senator, has been vying with Marco Rubio to emerge as the main alternative to Mr Trump.
Mr Cruz saw the Southern states that voted on Tuesday as his opportunity to stake his claim to the nomination, given their large evangelical Christian populations.
Mr Trump has won over many evangelicals, but Mr Cruz's campaign may be boosted by his victory in Texas, the biggest prize up for grabs on Super Tuesday.
Mr Rubio, a Florida senator who has become the favourite of much of the Republican establishment, has yet to win a primary, despite competing hard in Virginia.
He is putting hopes on his home state primary on March 15.
Mrs Clinton, the former secretary of state and senator, won in Texas, Arkansas, Alabama, Tennessee, Georgia and Virginia.
The wins reflected her strength in the South, where black voters are an important part of the Democratic base and overwhelmingly supporter her.
Voting was still going on in other contests or the races were too close to call.