White voters made up 72% of the electorate in the US presidential elections, with African Americans, Latinos and other minorities comprising a growing share, exit polls have indicated.

US President Barack Obama, who was reelected to a second term in office, received strong support from women voters as well as overwhelming support from African Americans and strong backing from Hispanic voters, exit polls suggest.

Analysts have commented that the profile of the voters is similar to the coalition that carried him to victory four years earlier to make him the nation's first African American president.

Obama withstood a late push by Romney in Pennsylvania and won battleground states of Ohio, Virginia, Wisconsin, New Hampshire, Iowa, Nevada and Colorado, according to projections.

One other battleground, Florida, remained too close to call early on Wednesday.

He also easily won traditional Democratic strongholds of California, New York and other populous states such as Michigan, the state where Romney was born and his father served as governor.

Democrats are expected to retain their majority in the Senate, while the Republicans earlier were projected to hold their majority in the US House.