Scattered voting problems, including machine glitches and long lines, emerged in some states on the biggest Super Tuesday ever held in America. But overall, voting appeared to go smoothly.
A record turnout was expected as an unprecedented 24 states held primaries and caucuses to narrow the field for the Democratic and Republican presidential nominee.
In the blue-collar Connecticut town of Manchester, just south of Hartford, turnout surged to nearly 70 per cent, forcing election officials to photocopy 3,000 ballots. Asked if he was surprised, registrar Frank Maffe Jr. replied, "Astounds me is more like it. It's amazing."
There were long lines in Minnesota, Georgia, Tennessee and Kansas. In Johnson County, the largest in Kansas, Democratic caucuses reported delays due to long lines and the relocation of one caucus because of overwhelming turnout.
There were similar crowds in Minnesota, where Democrats and Republicans waited in jammed hallways to cast caucus votes. Party officials said sites would stay open to accommodate every one in line as of 8.00pm, the cutoff time.
Precincts in Eastern Tennessee stayed open late so throngs of voters in line at closing time could cast ballots. Across the state, however, at least four counties had to close polls early because of tornadoes.
Long queues also affected Illinois. In Florida, election officials reported fielding hundreds of calls from confused people who apparently forgot - or were unaware - that Florida's primary was held last week.
Voters in Georgia, who are now required to present photo identification, were faced with lines of up to 90 minutes long. Poll workers were bogged down comparing IDs against computerized registration records.
By its nature, electronic voting is prone to both manmade and technical glitches. In the South, voting was affected by acts of nature.
Tornadoes also hit Arkansas. Natasha Naragon, a spokeswoman for the secretary of state's office, said several polling locations closed in northern Conway County.
In Arizona, where voting activists feared a controversial photo ID rule could cause confusion, things were apparently fine.
In the lead-up to Super Tuesday, voting advocates worried that long lines, high turnout and record numbers of mail-in ballots in states such as California could drag out the counting process for days. Across the country, election officials have estimated that mail-in ballots may account for as much as half of the vote in some areas.
More than five million people have requested mail-in ballots in California, where there are 15.7 million registered voters. Election officials in the most populated and delegate-rich state in the country have said results may not be available until tonight or later. As much as 25 per cent of the overall vote may go uncounted overnight, officials said.