Media playback is unsupported on your device Media caption Christine O'Donnell: 'Don't ever underestimate the power of we, the people'

The conservative Tea Party movement has won several victories over mainstream US Republicans in primary contests ahead of November's mid-term elections.

In one of the biggest upsets, Tea Party-backed candidate Christine O'Donnell beat a veteran congressman for the Senate nomination in Delaware.

A Tea Party candidate also won the race to stand for New York governor.

Republican strategists fear these candidates will not appeal to the wider electorate in November mid-term polls.

Seven states and Washington DC voted for candidates, in what is seen as a test of the mood within the parties.

Republicans are hoping to benefit from anger over the US economy to win both houses of the US Congress in November.

The grassroots Tea Party movement - which favours tax and spending cuts - emerged as a force in American politics only last year.

But observers say it has had a powerful effect on the Republican Party's choice of candidates for November and is seriously challenging the party's establishment.

Analysis Delaware tells you something important about the febrile state of US politics. It might even tell you something about the next presidential election. Republicans could win big, but some conservatives would rather have purity than power. This was Vice-President Joe Biden's Senate seat and it should be safe Democrat territory. But Democrats are so unpopular that polls indicated that if old-school Republican Mike Castle had won the nomination, he might have whisked it away from them. Both the polls and senior Republicans suggest that Tea Party favourite Christine O'Donnell hasn't a hope of winning the seat. But the Republican voters wanted her as their candidate nonetheless. So when people tell you that Sarah Palin will not win the nomination in 2012 because she cannot beat President Obama, remember it is grassroots Republicans who make that decision, not party strategists or commentators. What can Obama learn from DC vote? What impact will Tea Party wins have? US media reacts to Tea Party wins American voters on Tea Party surge

Tea Party-backed candidates had earlier won Senate nominations in Nevada, Colorado, Florida, Kentucky and Alaska.

The Tea Party triumph in Delaware is one of the most significant results of the entire primary season, says the BBC's Steve Kingstone in Washington.

Christine O'Donnell was publicly ridiculed and written off by the state's Republican leadership, but she survived to score a resounding victory over the establishment candidate, Congressman Mike Castle, our correspondent says.

It is a result that will ring alarm bells for the party leadership - Delaware is one of a handful of states where the Republicans must win if they are to seize control of the Senate, he adds.

Ms O'Donnell, a little-known marketing consultant who won in Delaware, had been endorsed by Sarah Palin, the Republican vice-presidential nominee in 2008 who has the support of Tea Party activists.

She told supporters at a victory rally that her cause was to "restore America".

"The people of Delaware have spoken. No more politics as usual," she said.

She will now compete in Delaware against Chris Coons, the Democratic candidate for a Senate seat formerly held by Vice-President Joe Biden.

We have to rise above this nastiness and unify for the greater good, because there's a lot of work to be done and there are a lot of people who want to get involved if the Republican Party would Christine O'Donnell

Before the result was known, Republican officials had warned that they would not fund Ms O'Donnell if she won the primary.

Speaking on Wednesday Ms O'Donnell accused the party of "Republican cannibalism".

"We have to rise above this nastiness and unify for the greater good, because there's a lot of work to be done and there are a lot of people who want to get involved if the Republican Party would," she was quoted by the Associated Press as saying.

Leading Republicans played down suggestions of a rift in the party.

"Let there be no mistake: The National Republican Senatorial Committee - and I personally as the committee's chairman - strongly stand by all of our Republican nominees, including Christine O'Donnell in Delaware," Senator John Cornyn said, in a statement.

Meanwhile, Democratic National Committee chief Tim Kaine said Ms O'Donnell's win "creates opportunities" for Democrats and was a sign of "civil war" in the Republican party.

DC Mayor ousted

In other results from Tuesday's polls, Tea Party ally Carl Paladino beat the Republican party's chosen candidate Rick Lazio in the race for the nomination to stand for New York governor.

The Tea Party movement The movement takes its name from the 1773 protest against British taxation, the Boston Tea Party, in which American colonists rebelled against attempts by Britain to impose parliamentary taxes on them without allowing the colonists representation in the British Parliament

The modern-day Tea Party is described as a grassroots movement that supports limited government and opposes high government spending

The informal movement is unified against President Barack Obama's healthcare proposals, his economic stimulus package and other aspects of his agenda

In Washington DC Mayor Adrian Fenty lost the city's Democratic primary to DC Council chairman Vincent Gray, just four years after sweeping into office with unprecedented support.

Other notable wins included:

In New Hampshire's Republican Senate primary, former state Attorney General Kelly Ayotte, backed by Sarah Palin, was declared the winner of a close contest with Tea Party-backed lawyer Ovide Lamontagne.

Embattled Congressman Charles Rangel won a Democratic primary in the race for his New York City seat, despite facing a number of accusations from the House ethics committee, most of them related to his personal finances

Former Maryland Governor Robert Ehrlich beat Tea Party-backed Brian Murphy for the Republican governor nomination in the state

Former Congressman Joseph DioGuardi won the Republican Senate primary in New York, after having to petition his way on to the ballot after failing to muster enough party support at the state convention.

Hawaii's primary on 18 September will be the last of the current primary election season.