Democrats vying for the right to challenge US President Donald Trump are turning their focus to Nevada and South Carolina after Bernie Sanders solidified his front-runner status with a narrow victory in New Hampshire, with Pete Buttigieg close behind him.

Mr Sanders, a senator from neighbouring Vermont, and Mr Buttigieg, a former mayor of South Bend, Indiana, finished first and second in the New Hampshire primary respectively.

The contest also showed the growing appeal of Senator Amy Klobuchar of Minnesota, who placed third after surging over the past few days.

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Two Democrats whose fortunes have been fading - Senator Elizabeth Warren of Massachusetts and former Vice President Joe Biden - limped out of New Hampshire, finishing fourth and fifth respectively amid fresh questions about the viability of their candidacies.

It was the second contest in the state-by-state battle to pick a Democratic nominee to face President Trump, a Republican, in the 3 November election.

Mr Sanders and Mr Buttigieg finished in a virtual tie in the first contest last week in Iowa and won an equal number of delegates - who formally vote at the party's convention in July to select a nominee - in New Hampshire, according to early projections.

The campaign's focus now begins to shift to states more demographically diverse than the largely white and rural states of Iowa and New Hampshire.

The next contest is on 22 February in Nevada, where more than a quarter of the residents are Latino, followed a week later by South Carolina, where about a fourth are African-American.

After that, 14 states, including California and Texas, vote in the 3 March contests known as Super Tuesday, which will also be the first time voters see the name of former New York City Mayor Mike Bloomberg on the Democratic presidential ballot.

Democrats must decide whether their best choice to challenge President Trump would be a moderate like Mr Buttigieg, Ms Klobuchar, Mr Biden or Mr Bloomberg - or a candidate further to the left like Mr Sanders or Ms Warren.

With an eye toward a potential election campaign, Mr Bloomberg announced the opening of a campaign office in New Hampshire.

He also picked up endorsements from three black members of the US House of Representatives after he came under scrutiny over past support for a policing tactic known as 'stop and frisk' that disproportionately affected racial minorities.

In New Hampshire, Mr Sanders drew 26% of the vote and Mr Buttigieg had 24%. Ms Klobuchar had 20%, Ms Warren 9% and Mr Biden 8%.

Pete Buttigieg

Mr Buttigieg said his strong results in Iowa and New Hampshire showed he had momentum going forward, "settling the questions of whether we could build a campaign across age groups and different kinds of communities."

His campaign said it would double its organising staff in Nevada to 100.

Mr Buttigieg also launched a new television ad in the state emphasising his healthcare proposal that would provide access to a government-run Medicare plan but let people keep their private insurance if they want.

He still faces questions about what opinion polls show is his weakness with black voters, one of the most loyal and vital Democratic voting blocs.

Former US Vice President Joe Biden had a poor showing in New Hampshire last night

The Democratic field shrank to eight candidates after New Hampshire.

Deval Patrick, 63, the former Massachusetts governor, dropped out, saying his poor showing in the state did not create "the practical wind at the campaign's back to goon to the next round of voting."

Businessman Andrew Yang and Senator Michael Bennet, who had trailed in the polls and also performed poorly in New Hampshire, also withdrew.

In a sign of the growing rivalry between Mr Sanders, 78, and Mr Buttigieg, 38, supporters of the senator booed and chanted "Wall Street Pete!" when Mr Buttigieg's post-primary speech was shown on screens.

Mr Biden, 77, was once the front-runner in the Democratic race, but stumbled to his second consecutive poor finish after placing fourth in Iowa.

He is certain to face growing questions about his ability to consolidate moderate support against a surging Mr Buttigieg and Ms Klobuchar.

Ms Klobuchar's campaign said it was spending more than $1m on ads in Nevada.