U.S. media reported Tuesday night that U.S. Senator John McCain has won the delegate-rich states of Ohio and Texas to secure the Republican Party's nomination for president.
On the Democratic side, it could be a long night, as Barack Obama - while winning in Vermont - faces a tough fight in Ohio and Texas against Senator Hillary Clinton.
U.S. media say the crucial Ohio Democratic race is too close to call. Voting had been extended in some areas in Ohio to accommodate the heavy turnout.
Early Texas voting shows Obama ahead but the state's two-step process of voting - primaries and caucuses - could mean the state may not be decided for several hours at least.
Clinton has strong support among Hispanics in Texas, while Obama's top backers in the state are from blacks and young people. Clinton, slightly behind Obama in the number of delegates needed to secure the Democratic Party nomination, hopes to halt Obama's winning streak.
In the small state of Rhode Island, whose polls have closed in the past hour, pre-election surveys showed McCain and Clinton ahead.
Some information for this report was provided by AP.
