A senior minister says it would be an "incredible feat" for the government to win any of the five "Super Saturday" federal by-elections on July 28.
The Australian Electoral Commission on Friday confirmed 41 candidates had nominated in total for the seats of Braddon, Mayo, Longman, Perth and Fremantle.
Eleven candidates have thrown their hats in the ring for the by-election in the Queensland seat of Longman, vacated by Labor's Susan Lamb over dual citizenship issues.
The Liberal Democrats' Lloyd Russell drew top spot on the ballot paper there, with One Nation's Matthew Stephen in fifth position, Ms Lamb in eighth spot and LNP's Trevor Ruthenberg ninth.
Education Minister Simon Birmingham said on Friday it had been more than a century since a government won a seat off an opposition in a by-election.
"Clearly it would be incredible feat to be able to do so now but we are working hard," he said, having visited Longman, Mayo and Braddon in recent weeks.
One Nation preferences will be crucial to winning Longman but leader Pauline Hanson said on Friday her party would not be urging voters either way.
"The political parties are putting out there that One Nation are directing our preferences to the Liberal party or we are directing our preferences to the Labor party - that's not true," she said, in a video.
"You own your preferences, not the political parties."
Asked whether the LNP could win without One Nation preferences, the prime minister told reporters in Longman the by-election was about whether voters supported Labor's "anti-business, higher-taxing agenda" or the coalition's plan for a stronger economy.
At the 2016 federal election, One Nation preferences split 52-48 in favour of the LNP in 12 Queensland seats.
Eight candidates have nominated for the Tasmanian seat of Braddon.
The Greens' Jarrod Edwards drew the top spot, with defending Labor candidate Justine Keay at the bottom of the ballot paper.
The Liberals' Brett Whiteley is in fifth place, with the Fishers and Farmers Party, two independents, the Liberal Democrats and the Australian People's Party also contesting.
Seven candidates have been confirmed for the South Australian seat of Mayo.
The Christian Democrats' Tracey-Lee Cane drew the number one spot on the ballot paper, with the Liberals' Georgina Downer fourth and defending candidate Rebekha Sharkie, from the Centre Alliance, fifth.
Labor's Reginald Coutts drew the last spot, with the Liberal Democrats, Greens and Australian People's Party also standing.
Perth has a field of 15 candidates, while seven are standing in Fremantle.
Labor is expected to win both, with no Liberal candidates nominating.
Candidates will also for the first time have to provide details of eligibility following the citizenship debacle that triggered four of the five by-elections.
The declarations will be published on the AEC website on Monday and early voting in all five seats starts on Tuesday.
The Labor and Liberal parties insist candidates have taken all steps to guarantee they are not in breach of the constitution.