Labour is bracing itself for heavy losses north of the border, as an exit poll suggested Ed Miliband's party would fail in its bid to become the largest party in the House of Commons.
The SNP could be on track for a record night, with the poll indicating Nicola Sturgeon's party could win all but one of the 59 Scottish constituencies.
According to the poll, the Conservatives could return 316 MPs nationally - 10 short of the number needed for an overall majority - while Labour was forecast to win 239.
The poll by GfK, NOP and Ipsos MORI on behalf of the BBC, ITV News, and Sky News, forecast that 58 of the 59 constituencies in Scotland would go to the SNP, who won just six seats in the last general election.
That could make them the third largest party in the House of Commons, with the Liberal Democrats reduced to just 10 MPs, according to the poll.
A total of 22,000 people in 141 polling locations in 133 constituencies throughout Great Britain were interviewed for the research.
The SNP leader said the exit poll result should be treated with caution.
Ms Sturgeon tweeted: ''I'd treat the exit poll with HUGE caution. I'm hoping for a good night but I think 58 seats is unlikely!''
Kezia Dugdale, deputy leader of the Scottish Labour Party, said she hoped the poll was ''badly, badly wrong'' because Scotland could not afford another five years of the Tories.
Tom Harris, Labour's candidate for Glasgow South, said he had heard from party workers at the count that he is likely to lose the seat he has held since 2001.
He told the BBC: ''I am told by my party workers who have been here longer than I have that it looks very unlikely that I will be resuming my seat on the green benches next week.
''The fact is there remains a great deal of resentment among those Labour voters who voted yes in the referendum against the Labour Party, which is seen rightly - and I'm proud of it - to have been an obstacle to independence.
''There came a point when those voters, even though they were Labour voters, decided that independence after all was actually the most important thing when it came to politics.
''They have chosen the nationalists over a party that I think is offering a very progressive, very left-wing, good case for government. But you know, that's democracy for you.''
As votes across Scotland were counted, cases of alleged fraud in a number of constituencies were being investigated.
Police Scotland have been informed of concerns over personation - where an individual votes as someone else either by post or in person at a polling station, as an elector or as a proxy - in Glasgow East, Cumbernauld, Kilsyth and Kirkintilloch, and in Edinburgh.
A City of Edinburgh Council spokeswoman confirmed concerns raised by polling staff had been reported to the police.
She said: "Polling staff raised concerns over two possible cases of voter personation. This was immediately reported to Police Scotland who are now investigating."
There were cheers when Alex Salmond, the former first minister and former SNP leader, arrived at the count for his Gordon constituency.
Mr Salmond, who is favourite to win the seat, smiled and appeared relaxed as he and his wife Moira arrived at Aberdeen Exhibition and Conference Centre, where the votes are being counted.
Labour's Michael Connarty said the SNP were going to pick up "upwards of 50%" of the votes in Scotland.
He launched a furious attack on the SNP, accusing the party of "betraying" and "duping" Scots.
The former Labour MP for Linthligow and Falkirk East, who looks set to lose his seat, said the SNP had misled people on its way to making huge gains.
He said the Nationalists' claim they could support a Labour government had won Nicola Sturgeon votes but damaged Ed Miliband's chances.
The SNP's team of MPs would be "largely irrelevant" at Westminister, he added.
He told BBC Scotland: "It looks like the SNP is going to pick up upwards of 50 per cent of the vote.
"They have basically betrayed the people of Scotland with their spin and I'll never forgive them for that. It is clear they have duped the people of Scotland."
He said Labour's proposals had been well received by voters but added: "It looks like people have been taken in by the cult of personality that is whizzing across Scotland at the moment."
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