Australia praises US diplomat Nikki Haley

Australia's foreign minister has paid tribute to the "highly capable, extremely impressive" US representative to the United Nations, who announced her resignation overnight.

Marise Payne heaped praise on retiring US ambassador Nikki Haley after seeing her in action on the floor of the UN in recent weeks.

"I think she leaves a very robust period as United States' ambassador to the United Nations, and I'm sure she has made a very significant impression," Senator Payne told ABC radio on Wednesday.

Former deputy prime minister Tim Fischer says Ms Haley would make an exceptional ambassador to Canberra, but conceded that is unlikely to happen.

"It appears Australia has to wait until after the (US) mid-terms in case Washington wants to send a defeated Republican to Canberra," Mr Fischer told AAP.

"It is totally unacceptable that it is more than two years since we had an ambassador."