Donald Trump has reached the number of delegates needed to clinch the Republican nomination for president.

Read more: Revealed: how Donald Trump's Scottish mother escaped New York and raised a US presidential candidate

His triumph completes an unlikely rise that has upended the political landscape and sets the stage for a bitter fall campaign.

Mr Trump was put over the top in the delegate count by a small number of the party's unbound delegates who told the AP on Thursday they will support him at the convention.

Read more: Obama says world leaders rightfully 'rattled' by Trump

It takes 1,237 delegates to win the Republican nomination for president - Mr Trump has reached 1,238. With 303 delegates at stake on June 7, Mr Trump will easily pad his total, avoiding a contested convention this summer.