WASHINGTON, United States (AFP) — Donald Trump and Ben Carson lead the Republican race for the US presidential nomination, with the two non-politicians together accounting for more than half the support from potential voters, a new poll showed yesterday.

The Washington Post-ABC News poll also found that Hillary Rodham Clinton, dogged by a controversy over her use of a private email server while serving as secretary of state, has steadily lost support over the past two months.

Though she still leads the Democratic field, potential voters gave her less than 50 per cent support for the first time in Post-ABC surveys, with her popularity dropping most among white women.

Trump was favoured by 33 per cent of registered Republican and Republican-leaning independent voters.

That marked a nine-point increase since mid-July and a 29-point jump since late May, before he announced he was running.

Trump got the most support in this survey from potential voters without a college degree and those with incomes below $50,000.

He was followed by Carson, with 20 per cent – 14 points more than in July. Other national polls have also shown him gaining more support since the first Republican debate last month.