Donald Trump's election as US president would trigger a collapse in support for Australia's alliance with the United States, according to a new poll.

Forty-five per cent of voters believe Australia should distance itself from the United States if it elects a president like Donald Trump, compared to 51 per cent who say the alliance should remain strong regardless.

"It's a striking and somewhat disturbing result because one of the strongest and most consistent polling results in the Lowy Institute's history has been support for the US alliance," executive director Michael Fullilove said.

In 2015, 80 per cent of Australian adults said the relationship was very or fairly important.