US Republican presidential candidate and New Jersey Governor Chris Christie looks on at his primary election night party Nashua, New Hampshire, in this February 9, 2016, file photo. Christie will end his campaign for the 2016 Republican presidential nomination, a senior aide said on Wednesday, a day after his disappointing sixth place showing in the New Hampshire primary. [Photo/Agencies]

WASHINGTON - New Jersey Governor Chris Christie and former business executive Carly Fiorina ended their presidential campaigns on Wednesday, narrowing the field challenging front-runner Donald Trump in the race for the 2016 Republican nomination.

Christie, 53, said in a Facebook post he was leaving the race "without an ounce of regret," a day after the combative Republican's sixth-place finish in the New Hampshire primary raised doubts about his viability as a candidate.

Fiorina, 61, a former Hewlett-Packard chief executive, said in a Facebook post she would suspend her campaign. The only woman in the Republican field placed seventh in New Hampshire, one of a series of state-by-state nominating contests for the Nov. 8 election to succeed Democratic President Barack Obama.

Trump's remaining opponents, most of them mainstream Republicans, will likely benefit from their departures, which leave seven Republicans from a field that once had 17 candidates.

Trump won the New Hampshire Republican primary by almost 20 points. The fifth-place finish of US Senator Marco Rubio of Florida, who had hoped to emerge as Trump's main rival after a surprise third-place showing in Iowa last week, leaves Trump without a clear challenger among the so-called establishment candidates.

On the Democratic side, US Senator Bernie Sanders of Vermont, a democratic socialist, easily defeated former Secretary of State Hillary Clinton in the New Hampshire primary.

The victories in both parties by candidates considered outsiders, testified to the sizable share of American voters upset over the slow economic recovery, immigration and America's place in the world and who are willing to shake up Washington.

Trump, 69, a billionaire businessman, has a double-digit lead over conservative Senator Ted Cruz of Texas in opinion polls for the next Republican contest, the South Carolina primary on Feb. 20, according to a Real Clear Politics average of opinion polls.

Christie poured much of his campaign's resources into New Hampshire and had considered a good showing there critical. He won only about 7 percent of votes on Tuesday, despite a pugnacious performance at a Republican debate last weekend.

"Christie needed to drop out. In short, he does not have the money or organization to be viable in South Carolina and beyond," said Monmouth University pollster Patrick Murray.

"Christie was certainly hurt by Trump stealing his 'telling it like it is thunder,' but Christie was also out-organized in the ultimate retail politics state," Murray said.