Vote counting has begun in the US state of South Carolina for the Republican presidential nomination. ABC News has called the race for former President Donald Trump.

Voting in the Republican Party's fourth nominating contest took place in the southern state on Saturday. Trump faced his ex-United Nations Ambassador Nikki Haley.

Haley was a former governor of South Carolina, her home state.

Trump has already won in three other states, taking a significant lead over Haley in the number of delegates secured.

His victory in his biggest rival's home state gives Trump a boost in securing the presidential nomination.

Haley previously has said she will not withdraw from the race after the South Carolina primary and will continue her campaign toward March 5, which is so-called Super Tuesday, when primaries and caucuses will be held in many states.