Long queues and malfunctioning machines marred the first hours of voting in some precincts across the US.
Some of the biggest problems today were in Georgia, a state with a hotly contested gubernatorial election.
Voters reported waiting up to three hours to vote.
At a polling place in Snellville, Georgia, more than 100 people took turns sitting in children’s chairs and on the floor as they waited for hours. Voter Ontaria Woods said about two dozen people who had come to vote left because of the queues.
At a poll site in Atlanta, voters waited in the rain in long lines that stretched around the building. Hannah Ackermann said officials at the polling site offered various explanations for the delay, including blaming workers who did not show up and overloaded machines.
Democrat Stacey Abrams will be the first black female US state governor if she is elected in Georgia in a tight race with Brian Kemp who is the Republican candidate.
President Donald Trump and vice-president Mike Pence campaigned for Mr Kemp while former president Barack Obama and talk show host Oprah Winfrey were among those to join Ms Adams on the campaign trail. The state has been strongly Republican in recent decades but is seen to now be a Democratic target.
Former president Jimmy Carter, who was governor of Georgia before his stint in the White House, has also backed Ms Abrams.