Rishi Sunak has said he accepts responsibility for the Conservative Party's historic general election defeat.
Sir Keir Starmer has led the Labour Party to a landslide victory and will take over from Mr Sunak as the UK's prime minister.
Mr Sunak told supporters: "The British people have delivered a sobering verdict tonight, there is much to learn... and I take responsibility for the loss."
Speaking in central London, Sir Keir said "change begins now", adding "it feels good, I have to be honest".
With more than 500 out of 650 seats declared, Labour is projected to form the next government, with a majority of 166.
The Tories are set for the worst result in their history. They have lost more than 170 seats and are forecast to be left with just 136 MPs.
Sir Keir told cheering Labour supporters the country was waking up to "the sunlight of hope" which was "shining once again on a country with the opportunity after 14 years to get its future back".
He added: “Now we can look forward – walk into the morning.”
Reform UK leader Nigel Farage won a seat in Parliament at his eighth attempt, in Clacton, promising "this is just the first step of something that is going to stun all of you".
Reform has four MPs so far - including chairman Richard Tice and former Tory Lee Anderson - and has finished second in many parts of the country, taking large amounts of votes from the Conservatives.
The Scottish National Party is now forecast to be reduced to just eight MPs, as Labour regains dominance in Scotland.
So far 18 Tory ministers have lost their seats, including Defence Secretary Grant Shapps, Commons leader Penny Mordaunt and former minister Sir Jacob-Rees Mogg.
The Liberal Democrats are benefitting from the collapse in Tory support and have got 64 MPs so far - the best result in their history. They have scored big in traditional Tory areas, including a win in Witney, former PM David Cameron's old seat.
Lib Dem leader Sir Ed Davey celebrated by dancing and singing to Sweet Caroline with supporters in central London.
Former Labour leader Jeremy Corbyn has defeated his old party to retain his Islington North seat as an independent.
But another high profile former Labour MP, George Galloway, failed to retain the Rochdale seat he won at a by-election in February, losing to Labour's Paul Waugh.
Carla Denyer, of the Green Party of England and Wales, has beaten Labour in Bristol Central and her co-leader Adrian Ramsay beat the Conservatives in Waveney Valley,. The party also held on to Brighton Pavilion, trebling their number of MPs.
Sir Keir Starmer's predicted landslide would be short of the 179 majority won by Tony Blair in 1997, with its vote share across the country up by just 2%, largely thanks to big gains in Scotland, according to polling expert Sir John Curtice.
But it will mean a Labour prime minister in Downing Street for the first time since 2010 and a battle for the future direction of the Conservatives if, as seems likely, Rishi Sunak stands down as leader.