Democratic presidential candidate Hillary Rodham Clinton was strongly supported by Hispanics and people seeking an experienced candidate, but Barack Obama was eating into her usual dominance of women and whites, in early national exit polls.
A coalition of black, young, white and higher-income voters were flocking to Mr Obama.
On the Republican side, preliminary data from exit polls of voters in 16 states showed Senator John McCain getting strong support from moderates and people valuing experience and leadership. He and Mitt Romney were battling for an edge among party regulars, while Romney was getting strong backing from the GOP's most conservative voters and people wanting a strong stance against illegal immigrants.
Mr Obama, an Illinois senator, was getting support from more than four in 10 women and about the same number of whites, leaving him just a few percentage points behind Mrs Clinton. That was a narrower deficit than he has faced in most states that have held nominating contests so far, with part of his strength coming from people under age 44, whom he was dominating.
In Oklahoma, a state Mrs Clinton won overall, there was no gender gap for her; she won among men and women. McCain won in New Jersey and Connecticut, where nearly half the voters were moderates and liberals who strongly support him. He also won in Illinois, a state dominated by conservative GOP voters, in part because Mr Huckabee and Mr Romney split most of the conservative vote, while the three rivals shared support from evangelicals.
Nationally, Mr Obama was getting the backing of eight in 10 blacks, his usual margin. But Mrs Clinton, a New York senator, was countering with strong support from Hispanics, about six in 10 of whom were supporting her. Much of that strength came from Hispanic women and from the oldest Latino voters.
Mr Obama was leading with liberals and had a modest advantage among white men, a group from which he has seldom received strong backing. Former Sen. John Edwards' decision to leave the race last week may have helped Obama with those voters.
Mrs Clinton had a clear lead with white women, with older white and Hispanic voters, and with lower educated people.
About half of Democrats across the country said they want a candidate who will change things. As usual Mr Obama was that group's overwhelming favorite, getting about seven in 10 of their votes. About one-fourth preferred experience, and Mrs Clinton was garnering virtually all of their votes.
Half of Democrats also named the economy as the country's top issue. Of that group, Mrs Clinton was favored slightly. She also led with those citing health care, while Mr Obama had an advantage with people most concerned about the war in Iraq.
The top issue for Republicans also was the economy, with four in 10 naming it. Those voters favored Mr McCain, as did those citing Iraq and terrorism. Mr Romney's advantage came with the one quarter who said illegal immigration was their main concern.
But on the economy, the message from GOP voters was mixed. On a separate question, MrRomney was cited as the candidate most trusted to manage the economy.
Mr McCain, the Arizona senator, and Mr Romney each had the support of nearly four in 10 people calling themselves Republicans. Mr McCain has yet to win that group of voters in any GOP contest this year, though he has tied for the lead among them before. He led among independents - a consistent McCain strength - though Mr Romney, a former Massachusetts governor, was not far behind.
Those preferring a candidate with strong leadership over agreement on the issues, and looking for experience, were tilting strongly toward Mr McCain. But nearly half of Republicans were looking for a candidate who shares their values. Mr Romney led with that group.
Mr Romney also had four in 10 votes from Republicans who want to deport illegal aliens, for a clear lead over Mr McCain.
Mr Huckabee, who has trailed the other two main candidates overall in recent national polls, had one-third of the votes of white, born-again and evangelical Christians, giving him a slight lead in that category over his rivals.