Donald Trump easily defeats Nikki Haley in her home state of South Carolina

Donald Trump is one step closer to the Republican presidential nomination after a massive win over Nikki Haley in South Carolina.

The former president won his primary opponent's home state by a 20-point margin, his fourth consecutive victory.

As he celebrated Mr Trump made no mention of Ms Haley, who vowed to stay in the race. Instead he set his sights on the general election in November.

That will be a likely rematch with his successor in the White House.

"We're going to look Joe Biden right in the eye," he told supporters minutes after US media projected him as the winner on Saturday night. "He's destroying our country - and we're going to say 'get out Joe, you're fired'."

Donald Trump's big primary victory on Saturday over Nikki Haley in her home state of South Carolina was the result of a ruthless and methodical campaign to eliminate her as a threat, according to aides and people close to both campaigns.

Despite having already secured a string of primary victories, it was crucial for Trump to win South Carolina, a key early Republican primary state that often predicts the party's nominee. Unlike in 2016, Trump was facing a rival who had won two terms as governor of the state and is still locally popular.

The plan was to isolate Haley politically by locking down endorsements from scores of officials in the state as quickly as possible to demonstrate publicly that she had no path to the presidency through South Carolina, aides with knowledge of the Trump campaign plan said.

Trump's victory on Saturday was not a complete blowout but he still defeated her by a comfortable 20 percentage points on her home turf.

As recently as December, Haley was still saying publicly that South Carolina was where she would finally score a win over Trump and turn the nominating contest around. Instead, it may be remembered as the state where her campaign suffered its fatal blow.

Ms Haley, who once served as a popular two-term governor of South Carolina, congratulated her opponent on his victory in her speech.

She promised not to quit, however, saying the roughly 40% of the vote she received was "not some tiny group".

"There are huge numbers of voters in our Republican primaries who are saying they want an alternative," she said, emphasising that her continued campaign was not about her own political ambitions.

"I'm not giving up this fight when a majority of Americans disapprove of both Donald Trump and Joe Biden," she added.

She has re-committed to staying in the race until at least Super Tuesday - 5 March - when voters in 16 states will cast their ballots on the same day.

"I'm a woman of my word," the former UN ambassador said. "We're headed to Michigan tomorrow, and we're headed to the Super Tuesday states throughout all of next week."