US business tycoon Donald Trump has announced he will run for the US presidency, confirming earlier speculation.

Mr Trump - who is a Republican - told Newstalk Breakfast last week: "It'll be something - we're going to have a wild time, because the United States should be doing much better than it's doing".

He came third in an opinion poll in the state of New Hampshire, which is often seen as decisive in shaping the national contest in the presidential election.