3:33 p.m. (14:33 GMT; 10:33 a.m. EDT)
Computer glitches have caused registration problems and disrupted voting for some in east London.
Some voters tweeted that when they arrived at the polling station Thursday, they were told they were not registered and unable to vote.
Hackney Council acknowledged some who registered online found that their information did not show up on their printed register. But it said almost all cases have been resolved, and that it was confident most locals will be able to vote without problems.
The BBC reported earlier that about 100 people in Hackney who had registered before the deadline were unable to vote because the computer system was overwhelmed.
2:18 p.m. (1318 GMT; 9:18 a.m. EDT)
Denmark's prime minister has appeared at a British polling station, though she wasn't voting.
Helle Thorning-Schmidt was in South Wales to support her husband, Stephen Kinnock, a Labour Party candidate for the constituency of Aberavon.
A video posted on YouTube showed the couple emerging from a polling station after Kinnock cast his vote early Thursday.
Asked how it felt to have a husband sitting in the parliament of another country, Thorning-Schmidt said she was happy for him because he worked hard campaigning.
"I don't know anyone who works as hard as Stephen," she said. "Today I am simply proud."
Asked how they would celebrate his win, she said: "Let's wait and see how things go today, but we will be very tense."
1:11 p.m. (1211 GMT; 8:11 a.m. EDT)
Many in the United Kingdom have been using social media to spread the news that they've voted.
Facebook said Wednesday that for the first time in a British general election, users have access to the "I'm a Voter" button. More than 1.3 million people had used it as of Thursday morning.
The social media giant said it believes the feature can encourage voter turnout.
The button has been used in past European elections and U.S. presidential elections.
12:45 p.m. (1145 GMT; 7:45 a.m. EDT)
About 50 million people are registered to vote in Britain's general election, with a record-breaking half-million applications pouring in on the deadline.
From March 1 to the April 20 deadline, more than 3 million people signed up, including 800,000 between the ages of 16 and 24. People can register when they're 16 but can't vote until they're 18.
In Scotland's capital, Edinburgh, officials said Thursday a majority of people who applied to vote by mail had already returned their ballots.
"We already have an 80 percent turnout for postal votes, which I think demonstrates the interest in the election," said Sue Bruce, returning officer for Edinburgh.
12:20 p.m. (1120 GMT; 7:20 a.m. EDT)
Some of Britain's leading actors and actresses are spending election day pretending to vote.
Judi Dench, Catherine Tate of "Doctor Who" and "Sherlock" co-creator Mark Gatiss are among the cast of "The Vote," which follows electors, candidates and officials at a London polling station.
James Graham's stage play is set in the final 90 minutes before polls close at 10 p.m. Thursday's final performance will air live on the More4 television channel, ending just as Parliament's clock tower delivers its 10 o'clock bongs.
Graham says it was surprisingly easy to convince some of Britain's leading actors to commit to a live-TV event where a lot can go wrong.
"These are all politically active artists," he said, "and most election nights they sit at home like everyone else, with a wine watching the Swingometer" - a results-measuring device that's a staple of BBC election-night coverage.
10:55 a.m. (0955 GMT; 5:55 a.m. EDT)
Several party leaders in Britain were out early at the polls to vote in the closest election in decades.
Prime Minister David Cameron and his wife Samantha voted at a polling station at his constituency in Oxfordshire while opposition leader Ed Miliband and his wife Justine swept past reporters as they voted in northern England.
Scottish National Party leader Nicola Sturgeon also came out early in Glasgow. She's not running for a place in the 650-seat Parliament, but her party is expected to win big in Scotland. That may help her become the kingmaker in deciding who runs the government.
Sturgeon has said she wants to make sure "the voice of Scotland is going to be heard more loudly at Westminster than it has ever been heard before," and that SNP supporters should join forces with Labour to lock out the Conservatives.
9:20 a.m. (0820 GMT; 4:20 a.m. EDT)
In the bright early-morning sunshine, voters are gathering to cast ballots at a polling station close to Parliament as police stand guard.
Signs of the unfolding political drama were all around. The squares opposite Parliament were packed with temporary outdoor television studios, while commuters picked up newspapers urging voters to the polls.
"It's going to be important for Britain for the next five years," said Gerry McQuillan, 61, an arts administrator voting Labour. "We're coming out of economic austerity but we've got to get the right government for the next five years."
Alexis Thomas, 34, a doctor, was mindful of all the predictions of a dead heat and wanted to make her voice heard.
"Because it's so tight, I think that if I didn't come out and vote, and didn't get the result that I wanted, then I'd only have myself to blame," Thomas said - though she wasn't saying what result that was.
7:50 a.m. (0650 GMT; 2:50 a.m. EDT)
Labour leader Ed Miliband has cast his vote in the U.K. general election.
He voted along with his wife, Justine, in the northern town of Doncaster, on Thursday morning. Miliband has represented the constituency of Doncaster North in Parliament for the past 10 years.
Miliband is the only politician with a realistic chance of taking the post of prime minister away from David Cameron, but neither of their parties is expected to achieve an overall majority in Parliament.
U.K. Independence Leader Nigel Farage also voted early in the southeastern constituency of South Thanet, and then tweeted: "I can't tell you who I voted for!"
7 a.m. (0600 GMT; 2 a.m. EDT)
Polls have opened in Britain's national election, a contest that is expected to produce an ambiguous result, a period of frantic political horse-trading and a bout of national soul-searching.
Prime Minister David Cameron's Conservatives and Ed Miliband's Labour Party are running neck-and-neck, and neither looks able to win a majority of Parliament's 650 seats.
Many voters are turning elsewhere - chiefly to the separatist Scottish National Party, which will dominate north of the border, and the anti-immigrant U.K. Independence Party.
Polls are open Thursday from 7 a.m. (0600GMT) until 10 p.m. (2100GMT). Most results are expected within a few hours.
Copyright 2015 The Associated Press.