Theresa May's future as Prime Minister and leader of the Conservatives was being openly questioned after her decision to hold a snap election disastrously backfired.
Mrs May pledged to offer "stability" if the Tories ended up as the largest party with the most votes - but yesterday's poll resulted in a hung Parliament, with no one able to establish a majority.
But Conservative former minister Anna Soubry said she should "consider her position" and take personal responsibility for a "dreadful" campaign and a "deeply flawed" manifesto after choosing to go to the country three years early in the hope of extending her majority.
Labour leader Jeremy Corbyn called on the Prime Minister to resign, saying she should "go and make way for a government that is truly representative of this country".
And former chancellor George Osborne, sacked from the Cabinet by Mrs May and now editor of the Evening Standard, told ITV: "Clearly if she's got a worse result than two years ago and is almost unable to form a government then she I doubt will survive in the long term as Conservative party leader."
With 606 out of 650 constituencies declared, a Press Association (PA) forecast predicted that Tories would end up with 319 seats - 11 fewer than when the election was called and seven short of an absolute majority. Labour was heading for 261 seats, the Liberal Democrats for 14, the Scottish National Party 34, Plaid Cymru three and Greens one, according to the PA analysis.
A BBC projection put the Tories on 43% overall - about six points up on David Cameron's result in 2015 - and Labour on 40%, outpolling Ed Miliband and Gordon Brown's results and even racking up more votes than Tony Blair did when he won power in 2005.
The pound plummeted as the shock figures set the scene for political turmoil at Westminster, disruption to upcoming Brexit negotiations and the possibility of a second election later in the year.
The night was marked by a collapse in Ukip support and a rash of high-profile losses for the SNP, as British politics returned to a two-party system on the greatest scale since the 1970s.
The Tories lost four frontbenchers, with Treasury ministers Jane Ellison and Simon Kirby and housing minister Gavin Barwell going down to defeat, along with Cabinet Office minister Ben Gummer, the author of the widely criticised Tory manifesto.
Ukip leader Paul Nuttall faced humiliation in Boston & Skegness, where he came in a distant third in one of his party's top target seats.
As Ukip voters switched to Labour and the Tories across the country, Mr Nuttall said Mrs May had put the Brexit process in "jeopardy" just 10 days before talks were due to begin in Brussels.
High-profile casualties of a night of shock defeats included Liberal Democrat former leader and ex-deputy prime minister Nick Clegg in Sheffield Hallam and SNP former first minister Alex Salmond in Banff & Buchan.
Home Secretary Amber Rudd and Education Secretary Justine Greening hung onto their seats by the skin of their teeth with much reduced majorities.
Accepting victory in Islington North, Mr Corbyn said voters had opted for hope and "turned their backs on the politics of austerity".
In an attack on Mrs May he said: "The Prime Minister called the election because she wanted a mandate.
"Well the mandate she has got is lost Conservative seats, lost votes, lost support and lost confidence.
"I would have thought that's enough to go, actually, and make way for a government that will be truly representative of all the people of this country."
Speaking as she was re-elected MP for Maidenhead, Mrs May said: "At this time, more than anything else, this country needs a period of stability.
"If, as the indications have shown and if this is correct, the Conservative Party has won the most seats and probably the most votes, then it will be incumbent on us to ensure that we have that period of stability and that is exactly what we will do."
Asked if Mrs May could remain as Tory leader, Ms Soubry told the BBC: "That is a matter for her. It is bad. She is in a very difficult place.
"She's a remarkable and very talented woman and she doesn't shy away from difficult decisions, but she now has to obviously consider her position."
Mrs May drove direct from the Maidenhead count to Conservative HQ in London, where she was hunkered down in talks with aides as dawn broke.
Labour deputy leader Tom Watson said the party would hold Mrs May to her campaign statement that if she lost six or more seats she would no longer be Prime Minister.
"Theresa May's authority has been undermined by this election," said Mr Watson.
"She is a damaged Prime Minister whose reputation may never recover."
Mr Osborne said there would be "a very big post mortem coming"
Liberal Democrats were celebrating the return of former ministers Sir Vince Cable, Sir Ed Davey and Jo Swinson two years after they lost their parliamentary seats.
And Tim Farron's party took Bath back from Conservatives and regained Caithness, Sutherland & Easter Ross and Edinburgh West, which were lost to the SNP in 2015.
Mr Farron held on to his Westmorland and Lonsdale seat in Cumbria on a much-reduced majority, down from 8,949 in 2015 to just 777 now.
Labour took Canterbury, a seat which had been held by Conservatives since 1918, and claimed Tory scalps in a string of seats including Bristol North West, Stroud, Warwick& Leamington, Stockton South and Vale of Clwyd.
Shadow foreign secretary Emily Thornberry said Labour "could form the next government" and would attempt to do so as a minority government if results allowed, rather than seeking to form a coalition with other progressive parties like the Lib Dems.
Foreign Secretary Boris Johnson, often tipped as a potential successor to Mrs May as Tory leader, said: "We've got to listen to our constituents and listen to their concerns."
Brexit Secretary David Davis dismissed suggestions he was a potential future leader, telling the Press Association: "That is behind me, I didn't run last time for a reason, I thought it's for other people now.
"The simple truth is we have a Prime Minister, she is a very good leader, I'm a big supporter of hers. I'll fight tooth and nail to keep her in place."
Further ministerial casualties included health minster Nicola Blackwood, who lost Oxford West and Abingdon to the Lib Dems, civil society minister Rob Wilson, who went down to Labour in Reading East, and James Wharton, whose Stockton South seat went to Mr Corbyn's party.
Mrs May's comments appeared to indicate she is preparing for the possibility of a hung parliament, after her massive gamble on a snap election backfired sensationally.