The Conservatives are set to win an overall majority of 86 in the general election, according to an exit poll for the BBC, ITV and Sky News.
The survey taken at UK polling stations suggests the Tories will get 368 MPs - 50 more than at the 2017 election - when all the results have been counted.
Labour would get 191, the Lib Dems 13, the Brexit Party none and the SNP 55.
The Green Party will still have one MP and Plaid Cymru will lose one seat for a total of three, the survey suggests.
The first general election results are due before midnight, with the final total expected to be known by Friday lunchtime.
In the exit poll. voters are asked to fill in a mock ballot paper as they leave the polling station, indicating how they have just voted.
The exit poll was conducted by Ipsos Mori at 144 polling stations, with 22,790 interviews.
Exit polls have proved to be very accurate in recent years. In 2017 it correctly predicted a hung Parliament, with no overall winner, and in 2015 it predicted the Conservatives would be the largest party.
This is the UK's third general election in less than five years - and the first one to take place in December in nearly 100 years - and has been dominated by Britain's 2016 vote to leave the European Union.
Conservative Party leader and Prime Minister Boris Johnson focused relentlessly on a single message: "Get Brexit done", promising to take the UK out of the EU by 31 January 2020 if he got a majority.
His main rival for No 10, Labour leader Jeremy Corbyn, promised voters another referendum with a choice between a renegotiated Leave deal and remaining in the bloc.
But Labour primarily campaigned on a promise to end austerity by increasing spending on public services and the National Health Service.
The Liberal Democrats promised to cancel Brexit if leader Jo Swinson became prime minister, but opinion polls suggested their vote was squeezed during the course of the campaign.
The Lib Dems did a deal with the Green Party and Plaid Cymru to stand aside in certain seats to maximise the pro-EU Remain vote.
The Scottish National Party said a strong vote for them would effectively be a mandate for a second independence referendum.
A decisive moment came early on in the campaign when Nigel Farage announced his Brexit Party would not be standing in seats won by a Conservative at the 2017 general election to avoid splitting the Leave vote.
The Conservatives began the campaign with a double-digit lead over Labour in the opinion polls, although this narrowed as polling day approached.
The Conservatives targeted their pro-Brexit message at those Labour constituencies in the Midlands and north of England which had voted to leave the EU in 2016.
Mr Johnson came under fire for avoiding scrutiny after declining to take part in a Channel 4 leaders' debate on climate change - and for ducking a half-hour prime time interview with the BBC's Andrew Neil, which the other party leaders had submitted to.
Follow election night on the BBC
- Watch the election night special with Huw Edwards from 21:55 GMT on BBC One, the BBC News Channel, and BBC iPlayer
- It will also be shown on BBC World News and streamed live on the BBC News website internationally
- As polls close at 22:00, the BBC will publish an exit poll across all its platforms, including @bbcbreaking and @bbcpolitics
- The BBC News website and app will bring you live coverage and the latest analysis throughout the night
- We will feature results for every constituency as they come in with a postcode search, map and scoreboards
- Follow @bbcelection for every constituency result
- From 21:45 GMT, Jim Naughtie and Emma Barnett will host live election night coverage on BBC Radio 4, with BBC Radio 5 Live joining for a simulcast from midnight