Two head-to-head polls released on Sunday showed a resurgent Hillary Clinton racing ahead in the US presidential race after a tumultuous month for Donald Trump, who has failed to rally confidence among voters or party leaders.

A Washington Post-ABC News poll showed a 12 point lead for the Democrat, her largest advantage since the autumn and a dramatic improvement over last month when the poll showed her almost tied with Trump.

If the presidential election were held today, 51 per cent of respondents said they would vote for Clinton, versus 39 per cent for Trump.