The by-election in the Queensland federal seat was triggered by the resignation of former minister Stuart Robert.
The latest figures from the Australian Electoral Commission show 13,291 people have cast an early vote while 6288 postal votes have been returned out of 18,710 applications.
Postal vote applications close on Wednesday.
The Liberal National Party is confident of holding the seat, putting up local councillor Cameron Caldwell as its candidate to replace Mr Robert.
But there are concerns of a possible voter backlash following the release on Friday of the robodebt royal commission report.
Mr Robert, as minister, was found to have made misleading public comments about the unlawful scheme.
But the ex-minister noted in response he had "worked hard to get the legal advice and close down the income compliance scheme" and confirmed he had not been included in a confidential report section which was referred to authorities including federal police.
The LNP has been campaigning hard on the rising cost of living and voter unrest over the Indigenous voice referendum proposal.
Labor is running nurse educator Letitia Del Fabbro, who previously contested the 2022 election.
A total of 13 candidates are on the ballot paper.
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