The Conservatives are set to be the largest party but without an overall majority according a joint BBC/Sky/ITV exit poll, which indicated the Tories will win 314 seats and Labour 266.
The BBC/Sky/ITV poll suggested the UK was heading for a hung parliament, with Conservatives 12 seats short of the 326 they need for an absolute majority in the Commons.
The poll put Tories on 314 seats, with Labour on 266, the Scottish National Party on 34, Liberal Democrats on 14, Plaid Cymru on three and Greens on one.
If borne out by the actual results, the poll figures would represent a humiliation for the Prime Minister, who went into the election with a small but viable majority and expectations that she should be able to secure an advantage of 100 seats or more in the House of Commons by going to the country early.
And it would be a personal triumph for Labour leader Jeremy Corbyn, who was widely regarded as having run a successful campaign after being written off as unelectable by many observers and some in his own party.
General Election 2017: Live news & reaction in Yorkshire and across the UK
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It would also represent a significant setback for the SNP's Nicola Sturgeon, whose party won a historic 56 out of 59 seats north of the border just two years ago.
And it could throw the UK's politics into disarray as the parties scrabble to form a government, just 11 days before the expected start of Brexit negotiations in Brussels.
The poll suggests the Tories will lose 16 of the 330 seats they held at the end of the last Parliament, while Labour gains 37, the SNP loses 20 and the Liberal Democrats gain five.
However, even after 30,000 voters were questioned at 144 polling stations, there is always a possibility that the exit polls may be misleading.
In 2015, they significantly underestimated the Tory tally, putting David Cameron's party on 316 when it finally emerged with 331.