London (AFP) - Millions of Britons were voting Thursday on whether to stay in the EU or quit, in a momentous referendum that has polarised the country and could change the face of Europe.
The evening wave of voters headed to cast their ballots after work before the polls close at 2100 GMT, after a close-fought and often vitriolic campaign focused on immigration, the economy and Britain's very identity.
A record 46.5 million people registered to vote in the once-in-a-generation referendum being nervously watched across Europe and the world.
European leaders fear a so-called Brexit would trigger the biggest crisis in the 60-year history of post-war integration on the continent.
The final opinion polls put the "Remain" camp narrowly ahead and financial markets duly bet on a vote to stay Thursday, with world stocks surging and the pound hitting its highest level this year.
London's benchmark FTSE 100 share index closed up 1.2 percent at 6,338.1 points, while key eurozone indices in Frankfurt and Paris forged even higher, at around two percent up.
In currency trading, the pound hit a 2016 high against the dollar at $1.4947.
An Ipsos MORI opinion poll for the London Evening Standard newspaper put "Remain" on 52 percent and "Leave" on 48 percent.
- Turnout crucial -
Experts predict a high turnout across the kingdom.
Jenny Watson, who chairs the Electoral Commission referendum overseers and will announce the official result, said recounts would not take place "simply because the vote was close".
"If it's a dead heat then it's a dead heat. There is no casting vote," she told the BBC.
While early indications of results could come from around 0200 GMT Friday, the final declaration is not likely until around 0800 GMT.
Leave figurehead Boris Johnson, the former London mayor, said the race was "very close", as he returned to the British capital from Edinburgh, but added: "From what I have heard... turnout is good in areas where we need it to be."
In London and southeast England, many voters braved torrential rains and thunderstorms to have their say.
Several polling stations had to be relocated due to flooding and one was being run on a generator due to a power outage.
The referendum asks: "Should the United Kingdom remain a member of the European Union or leave the European Union?"
Commentators suggest Brexit could trigger a constitutional crisis in Britain, prompting another Scottish independence referendum.
There are also fears it could prompt other EU countries, disillusioned with how Brussels has handed the eurozone and migrant crises, to try to break away.
- Voting in a launderette -
Polling stations have been set up at locations including churches, schools and even a launderette and a windmill.
Outside a polling station in suburban Biggin Hill, south of London, 55-year-old Steve Annett, who works in publishing, said: "We're stronger together working with our European neighbours.
"Obviously the economy is a major concern," he told AFP.
Meanwhile pensioner Wendie said older people were "fed up of being taken over, our laws being taken over by the EU. Why can't we rule our own country?"
Thousands of people queued to vote in the British overseas territory of Gibraltar, which borders Spain.
Gibraltar's mayor Adolfo Canepa told reporters he was worried about the future if Britain left the EU.
"I know what it was like to live for all those years when the frontier was closed and I wouldn't like to put my children and grandchildren through that again," he said.
The often acrimonious campaign has exposed a wide gulf between Britons on the country's often troubled four-decade membership of the European club.
EU leaders have warned Britain -- the world's fifth-largest economy -- that there would be no turning back from a vote to quit.
"Out is out," European Commission chief Jean-Claude Juncker said Wednesday, dismissing any talk of a post-vote renegotiation of Britain's membership terms.
In many European countries, newspapers pleaded "Please don't go" while several monuments were lit up with the British flag.
- Cameron invokes Churchill -
Prime Minister David Cameron, who faces calls to resign in the event of a "Leave" victory, voted early without making any comment.
At his final rally on Wednesday, the Conservative leader implored people to stay in the bloc, invoking Britain's cigar-chomping wartime prime minister Winston Churchill.
"Churchill didn't give up on European democracy... and we shouldn't walk away," he said.
Nigel Farage, leader of the anti-EU UK Independence Party, said as he voted that "Leave" had "a really good, strong chance".
"It's all about passion, it's all about who cares enough to go out and vote."
The referendum battle was shaken by the brutal murder of Jo Cox, a pro-"Remain" Labour lawmaker and mother of two who was stabbed and shot in the street one week before the vote.
Thomas Mair, 52, has been charged with her murder and had a provisional trial date set for November at a court hearing on Thursday.
EU leaders will begin a two-day summit Tuesday to deal with the outcome and decide how to cope with the risk of similar referendums on the continent.