The anti-immigration party's communications director Patrick O'Flynn, who was elected an MEP for the East of England tonight, said his party had done something "quite unprecedented".
Speaking as he celebrated his election, the former journalist said: "we want our country back and we are going to have a really good crack at getting back. The British people have spoken, they want control of their nation."
"The political earthquake is underway tonight," he added. "Any party that doesn't hear the message loud and clear is in for another shock less than a year from now when we fight again at the general election."
Labour sources conceded earlier on Thursday that Ukip was likely to win the UK contest, with eurosceptic parties across the continent expected to prosper as voters express their anger at the financial crisis which has crippled many countries in the 28-member bloc.
Farage said tonight Ukip was on track to win the elections, which "will be an earthquake because never before in the history of British politics has a party seen to be an insurgent party ever topped the polls in a national election."
If the result is confirmed as a Ukip win, it would be the first time since 1984 that the Westminster Opposition party, in this instance Labour, has failed to top the poll in the European elections.
David Cameron, Ed Miliband and Nick Clegg have all faced criticism over the way they have responded to Ukip's rise and strategists will study the results of the final national ballot ahead of next year's general election as they plan how to tackle a new era of four-party politics.
Being pushed into second place in a national poll with just 12 months to go until the general election will add to questions about Miliband's ability to take the keys to No 10.
A senior Labour source said although it looked as if Ukip was ahead, the vote for Miliband's party was "up significantly" on the 15.7% it achieved in 2009.
Clegg - who has acknowledged the Liberal Democrats could lose all of their 11 MEPs - is facing MPs' questions over his leadership and calls to quit from activists, including general election candidates.
Cameron has been urged by influential Tory MP David Davis to bring forward his promised EU referendum by a year to 2016 to persuade defectors to Ukip that he is serious.
Tory Cabinet minister Philip Hammond has insisted the vote was skewed by a significant number of "lender voters" who would abandon Ukip and return to the Conservative fold for the 2015 general election.
Hammond told Sky News: "Ukip is a protest party. Most of the people who are voting for Ukip - not all of them, but most of them - are disillusioned voters of other parties who have moved to Ukip to send us a message, and we've got a year to show them that we've got that message.
"We've got to reiterate our continuing story about how our economic plan is delivering for Britain, recognising that not everybody is feeling the benefit of that yet. We've got to make sure they do and we've also got to express the specific concerns that people are articulating about immigration and about Europe."
LOCAL ELECTION RESULTS: Fantastic Mr Farage: Jubilant Ukip Send Feathers Flying
Work and Pensions Secretary Iain Duncan Smith told the Sunday Times that on the doorstep "most people have no idea" that Cameron had pledged to allow a public vote on the EU.
Davis said the policy lacked "both clarity and credibility" and should be speeded up to allay the fears of voters who have defected to Ukip.
But asked about the 2016 proposal, Defence Secretary Hammond told the Murnaghan show: "I personally don't think that makes sense.
"I think if we are going to renegotiate the relationship that Britain has with the European Union, we should do that as a serious exercise, working with countries like Germany, the Netherlands, the Scandinavian countries, who are also deeply concerned about these issues. There's an earthquake going on in Europe, it's not just Britain."
Senior Lib Dems rallied around Clegg in response to calls for him to quit as leader to avert an electoral mauling next year.
Liberal Democrat president Tim Farron appealed for an end to the "absolutely foolish" calls for Clegg to fall on his sword and former leader Lord Ashdown said ousting the Deputy Prime Minister was "just about the silliest idea I have heard, I think, in my political career".
Southport MP John Pugh suggested that a dozen of his Commons colleagues had expressed doubts about whether Clegg should continue at the head of the party.
Pugh told the Sunday Times an internal "post-mortem" of the poor night at the polls - which saw the party almost or entirely wiped out in some former strongholds - "has to include a truly open, mature and balanced look at our whole strategy, including the leadership issue".
Colleague Adrian Sanders, who represents Torbay, said: "The problem is the messenger, very few people say it's the message."
Ex-MP Sandra Gidley - one of around 250 people to have signed an online letter demanding a change of leader - said Clegg was tainted by his position in the Tory-led coalition.
But Farron - a favourite to succeed Clegg - told BBC1's Andrew Marr Show: "Nick Clegg should undoubtedly stay and the Liberal Democrats should stay the course in government."
Lord Ashdown told BBC's Sunday Politics: "This is the moment when we need to get out with a really good message and campaign through the summer in the context of the general election and we spend it on an internal, totally unnecessary, divisive leadership election? I think that's ridiculous."
The former leader, who is chairing the party's 2015 election campaign, said Clegg was "the best prime minister Britain hasn't got".
Although Labour won more than 300 seats in the local election contests, the party failed to break through in some areas which will form key battlegrounds next year.
Miliband said: "There is a deep sense of discontent with the way our country is run. I am determined to show people, including those who voted for Ukip, that we can change our country so they can build a better life for themselves and their family.
"In the weeks and months to come, you will see our policy review finalising our programme for changing our country so we can connect the wealth of our nation to the lives of working people once again."
The European Parliament website predicted a turnout of 36% in the UK, where votes were cast for MEPs on Thursday at the same time as council elections in parts of England and Northern Ireland.