Republican presidential candidate Mitt Romney told his supporters in Boston, Massachusetts he was confident of victory "all the way to the White House".
Republican presidential candidates Mitt Romney and Rick Santorum are locked in a tight battle for the state of Ohio, Super Tuesday's most coveted prize, BBC reports.
Mr Romney won the contests in Idaho, Massachusetts, Vermont and Virginia, while Mr Santorum prevailed in Oklahoma, North Dakota and Tennessee.
Meanwhile, Newt Gingrich declared victory in his home state of Georgia, and Alaska was still voting. The eventual nominee will challenge Barack Obama in November's election.
The contest has gone down to the wire in Ohio, where just a few thousand votes separate Mr Romney and Mr Santorum.
Ohio has symbolic importance as no Republican nominee has ever become president without winning the crucial swing state in a general election.
