Sharkie to romp Mayo by-election: poll

Centre Alliance candidate Rebekha Sharkie will romp to victory in the Mayo by-election while Labor's Susan Lamb has a 50 per cent chance of retaining Longman, a new poll shows.

The ReachTel/Australian Institute survey found Ms Sharkie ahead 62 per cent to Liberal candidate Georgina Downer's 38 per cent on a two-party preferred basis in the South Australia seat.

Ms Lamb was neck and neck with LNP candidate Trevor Ruthenberg in her Queensland seat.

Both Ms Sharkie and Ms Lamb fell foul of the dual citizen debacle that has ripped through the parliament.

The by-elections will be held on July 28 and on the same day as three others in what has been dubbed "Super Saturday".

The poll was taken last Thursday evening, after the Turnbull Liberal government had successfully steered its personal income tax cuts package through the Senate.