Boris Johnson is on course for a landslide victory in the General Election and Jeremy Corbyn says he will not lead Labour into the next election as his party suffered the worst result in decades.
With the vote still being counted, a Sky News projection estimates the Tories have secured between 363 and 369 seats.
Labour are projected to win between 193 and 199 seats, which would be the party's worst result in decades.
Speaking after he held onto his Uxbridge and South Ruislip constituency, Mr Johnson said: "It does look as though this One Nation Conservative government has been given a powerful new mandate to get Brexit done."
- Tories on course for biggest victory since Margaret Thatcher in 1987
- Labour set for worst result since 1935
- SNP tightens grip of Scotland and calls for second independence referendum
- Liberal Democrat leader Jo Swinson loses her seat to SNP, to speak later
- "Red Wall" crumbles as string of Labour seats go to Tories
- Chuka Umunna, Dominic Grieve and Anna Soubry among those who lose
Jeremy Corbyn announced he would not lead Labour in any future general election campaign after a "very disappointing" night.
But he suggested he would not be departing as Labour leader immediately.
"I will discuss with our party to ensure there is a process now of reflection on this result and on the policies that the party will take going forward," Mr Corbyn added.
"And I will lead the party during that period to ensure that discussion takes place and we move on into the future."
Sky News' forecast result would provide the prime minister with thumping vindication of his decision to push for the first December election since 1923.
It also puts the UK on course to leave the EU on 31 January, after Mr Johnson campaigned on his promise to "get Brexit done".
The SNP is forecast to win as many as 55 seats, with leader Nicola Sturgeon saying: "The people of Scotland have made very clear that they don't want Boris Johnson as prime minister, that they don't want Brexit, and they want Scotland's future to be in Scotland's hands."
Liberal Democrat leader Jo Swinson lost her East Dunbartonshire seat to the SNP, with her party expected to make few gains from their 2017 general election result, having started the campaign with high expectations.
Labour's much-vaunted "red wall" of safe seats across the Midlands and the North appears to have crumbled in the face of the Tories' pro-Leave position.
Blyth Valley in Northumberland, Workington in Cumbria and Wrexham in Wales were all among former Labour strongholds to fall to the Conservatives.
Despite being held by Labour since 1950, Blyth Valley turned blue thanks to a 10% swing.
And Workington, which had taken on symbolic status as a Conservative target seat in the election campaign, was won by the Tories with a similar swing.
The constituency had previously been held by Labour for 97 years out of 100 since its creation.
Sedgefield, the former constituency of ex-prime minister Tony Blair, was also won from Labour by the Tories.
Echoing the lyrics of Labour's campaign song from their 1997 landslide win under Mr Blair, the Conservative Party's Twitter account posted after the result was announced: "Things can only get better."
There were suggestions the Tories could have enjoyed even greater success in some areas, if it were not for the presence of the Brexit Party.
However, despite their success in gaining Labour-held seats, the Tories appeared to have struggled in Remain-supporting areas.
Putney, the London seat won in 2017 by former Conservative minister Justine Greening, was taken by Labour with a 6% swing.
And the Liberal Democrats won St Albans from the Conservatives with a 10% swing.
After losing a string of seats to the Tories, Mr Corbyn's close allies calling for an inquest into the party's election result.
Richard Burgon, Labour's shadow justice secretary, told Sky News: "We need a sober, serious analysis over the next 24 hours or so."
His fellow Labour frontbencher Dawn Butler, Labour's shadow women and equalities secretary, said: "We really have to reflect quite seriously about where we go and the direction of travel for the Labour Party."
And Ken Livingstone, the former London mayor and ex-Labour MP, admitted Mr Corbyn was likely to go.
"It looks like the end for Jeremy, which is disappointing for me since I'm a close ally. I'm sure he'll have to resign tomorrow," he said.
Labour's Ruth Smeeth, who predicted she was about to lose her Stoke-on-Trent seat where she was standing for re-election, told Sky News that Mr Corbyn "should announce he's resigning as leader of the Labour Party from his count today.
"He should have gone many, many, many months ago."
Ms Smeeth, a former parliamentary chair of the Jewish Labour Movement, added: "Jeremy Corbyn's actions on antisemtism have made us the nasty party.
"We are the racist party."
But Momentum - the left-wing group that grew out of Mr Corbyn's two successful Labour leadership campaigns - vowed to "keep the Labour Party socialist" in the face of the election result.
Laura Parker, Momentum's national coordinator, said: "It's unquestionable that Labour's policies are popular.
"Every poll shows it, and there is absolutely no appetite to go back to the centrist policies of old.
"But in this election we were squeezed by Brexit and it was the defining issue.
"Against that storm we built a huge movement of thousands of ordinary people and they won't stop until we see real change in this country."
One of those touted as a possible successor to Mr Corbyn, shadow minister Laura Pidcock, lost her Durham North West seat to the Tories.