Australian by-election a litmus test for right-wing One Nation Party

Polls have opened in a key by-election in regional Australia, viewed as an electoral test of support for the right-wing populist One Nation party, which could win its first federal lower house race.

The contest in Farrer, a vast regional electorate in New South Wales, was triggered by the resignation of Sussan Ley, who quit when she was ousted as the opposition conservative Liberal Party leader after nine months.

While the Liberals are running a candidate to replace Ley, opinion polls suggest it could be a close contest between local independent Michelle Milthorpe and One Nation's David Farley.

Voting booths close at 18:00 local time (09:00 BST) on Saturday, with results expected shortly after.

Milthorpe, a local teacher, came second in the two-candidate preferred count at last year's federal election against Ley, who recorded her worst result as a sitting MP since she first won the seat in 2001.

Australia has a preferential voting system where voters rank candidates from their most to least preferred. The final tally is calculated as a challenge between two candidates after preferences are distributed, known as the two-candidate preferred count.

While the by-election result will not affect the Labor government's massive majority, it could see the first One Nation MP elected to Australia's national parliament.

Saturday's poll is the first federal test of One Nation's support after the party recorded the second-highest number of votes out of any political party in the South Australian state election in March – its best ever electoral performance.

One Nation has never won a federal lower house contest. In the late 1990s leader Pauline Hanson initially held her seat as an independent before losing her re-election bid. She has since returned to the parliament as a senator.

The party chose David Farley, former CEO of the Australian Agricultural Company, a large beef producer, to run in Farrer.

In a campaign video shared on social media, Farley said he had "lost a bit of faith" in the major parties. "They say one thing to your face and then go and do something else in parliament," he said.

Farrer spans 127,000 sq km (49,000 sq miles), an area larger than South Korea, and takes in the regional centres of Albury, Griffith and Deniliquin. The seat has always been held by either the Liberal or National parties.

Saturday could also be the first time neither of the two major parties – Labor and the Liberal-National Coalition – ends up in the two-candidate preferred count at a federal election. Labor is not contesting the race.

The by-election marks the first electoral test for the new leaders of the Liberal and National parties, respectively Angus Taylor, who ousted Ley in February, and Matt Canavan, who replaced David Littleproud in March.

The Liberal-National coalition suffered its worst ever defeat in last year's federal election, and the two parties have struggled with infighting and poor polling since then.