As the US presidential election race enters its final hours, people across the country are turning up to vote early.

Who is choosing the US President.

Lines of people waited to cast their ballots at early-voting centers in Ohio, Florida and Indiana. Some 30 million people have already voted in 34 states and the District of Columbia. Their votes will be counted on Election Day, Tuesday.

Under the US voting system, the winner is not determined by a nationwide popular vote but in state-by-state contests.

There are nine "battleground" states that don't consistently vote Republican or Democratic. Winning their votes is extremely important in this tight presidential race.

Most opinion polls indicate President Barack Obama has a slight edge over Republican candidate Mitt Romney in these crucial swing states.