The results so far: Douglas Alexander, Jo Swinson and Jim Murphy lose their seats

Nationalist Kirsten Oswald took the party from fourth to first to oust Mr Murphy in East Renfrewshire, ending his 18 year career as an MP

With some constituencies showing swings to the SNP of more than 30%, Mr Alexander, Labour's election campaign chief, was the first big scalp of the night for the nationalists.

Student Mhairi Black, 20, beat the former government minister in Paisley and Renfrewshire South, the seat he had held since 1997.

In Kirkcaldy and Cowdenbeath, which had been the safest Labour seat in Scotland, the SNP easily overturned a majority of more than 23,000 to capture the constituency which had been held by former prime minister Gordon Brown, who did not stand again.

As an SNP landslide swept across the country, Labour candidate Kenny Selbie polled 17,654 votes, nearly 10,000 fewer than nationalist Roger Mullin, who picked up 27,628 votes for the SNP.

Shadow Scottish secretary Margaret Curran lost her Glasgow East to the nationalists, who appear to be on track to pick up all seven constituencies in the city.

Mr Murphy said it was an "enormous" moment for the SNP, but vowed that his party's fightback starts tomorrow.

He insisted: "The fight goes on and our cause continues.

"I know hundreds of thousands of Scots still believe in the progressive policies the Labour party stands for.

"The Scottish Labour party has been around for more than a century. A hundred years from tonight we will still be around.

"Scotland needs a strong Labour party and our fight back starts tomorrow morning."

Ms Sturgeon, the Scottish First Minister, said Labour had been "losing the trust of the people of Scotland over a period years".

She told the BBC: "What we're seeing tonight is Scotland voting to put its trust in the SNP to make Scotland's voice heard, a clear voice for an end to austerity, better public services and more progressive politics at Westminster. That's what we now intend to do."

Throughout the election campaign, Ms Sturgeon had been hoping to form a "progressive alliance" with other parties to bring about change at Westminster.

But with the Conservatives on track to be the largest party again, she insisted Labour could not blame her party for its failure to win across the UK.

Ms Sturgeon said: "I hope we're not looking at another Conservative government, but if we are then it will be more important that there are strong SNP MPs in Westminster, making Scotland's voice heard and making sure Scotland's interests are protected."

With more than 30 SNP MPs now elected, the nationalists have had a record breaking night at Westminster, winning more than half the 59 constituencies north of the border.

In 2010 it had won just six seats, while previously its best ever result had been in October 1974, when 11 SNP MPs were returned to the House of Commons.

The tone was set when nationalist Alan Brown won the first seat of the night in Scotland, with 30,000 votes.

That saw him unseat Labour's Cathy Jamieson to become the new MP for Kilmarnock and Loudoun.

Mr Alexander had had a majority of more than 16,000 going into the election, but Ms Black - who is likely to be the youngest MP - easily overturned that.

She polled 23,548 votes, ahead of Mr Alexander, who had 17,864.

Speaking immediately after the result was declared, Mr Alexander said: ''This of course has been a very difficult night for Labour.

''Scotland has chosen to oppose this Conservative government, but not place that trust in the Labour party.

''It will be our responsibility to re-win that trust in the months and years ahead.''

Ms Curran said: "It's not a great night for the Labour Party but I will tell you one thing that I absolutely believe, there is great social and economic injustice in Scotland.

"Tonight, I think, has been a clash of nationalisms.

"To me, the bigger cause, the greater cause, is equality and you will always need a Labour Party to fight that."

She added: "The Labour Party absolutely believes that we need to stand by working people. Of course we understand that they have given us a message tonight, but we will never lose that deep belief in the cause of economic and social equality.

"And the Labour Party, when it gets down to thinking about that, that's how we'll come back."

The SNP also claimed the seat of UK business minister Jo Swinson, who lost the East Dunbartonshire seat she had held for the Liberal Democrats since 2005.

Former nationalist leader and Scottish first minister Alex Salmond said it looked like his party would win a ''very large number'' of seats.

Mr Salmond, who is hoping to win the Gordon seat, told the BBC: ''The winds are blowing across Scotland and they're blowing very strongly, believe me, in the north east of Scotland.

''There's going to be a lion roaring tonight, a Scottish lion, and it's going to roar with a voice that no government of whatever political complexion is going to be able to ignore.

''I think it's going to be a resounding voice, a clear voice, a united voice from Scotland, and I think that is a very good thing.''

He said there was an ''electoral tsunami'' in Scotland

Mr Salmond told ITV that if the exit polls, which predict the SNP securing all but one seat in Scotland, were correct ''it certainly leaves David Cameron, if that were the case, with no legitimacy whatsoever up in Scotland''.

Natalie McGarry, who ousted Ms Curran to become the new MP for Glasgow East, said the SNP had had "a fantastic campaign in the east Glasgow".

She added: "We have spoken to so many people in different communities right across the east end and we think that we've had a message that's resonated with them."

Meanwhile the SNP's Patrick Grady, who took Glasgow North earlier in the night, said: "It is the greatest honour to be the first SNP member of parliament ever elected in Glasgow in a general election."

Labour's Ian Davidson, who lost his Glasgow South-West seat to the SNP, said Mr Murphy could not now continue as leader and called on him to resign.

He told the BBC: "He was elected as party leader on the basis that he was an MP. Only MPs and MSPs can stand for the leadership.

"Morally, as the man who has led us to the biggest ever disaster that Labour has suffered in Scotland ... of course he can't continue.

"The process of rebuilding the Labour party has got to start with an examination of both personnel and ideas.

"And therefore Jim has got to do the honourable thing and resign. I'm sure once he has got time to reflect, he will do that."