Less than four months after the Victorian state election, voters in Gippsland South will return to the polls this Saturday to replace long-serving Nationals MP Peter Ryan.

The by-election, to be held on Saturday, was triggered by the resignation of Mr Ryan, who announced his retirement after more than 20 years in the job.

The party elder has backed upper house Nationals MP Danny O’Brien as his successor.

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Mr O’Brien has stood down from the Legislative Assembly and risked his position for a chance of taking the Lower House seat.

While Gippsland South is a traditionally conservative electorate, Mr O’Brien said it was far from a safe seat, especially with a Liberal party candidate in the race.

“Some would say that yes, it’s a safe seat, people always vote that way. I’d argue people vote that way because the Nationals have given good service,” Mr O’Brien said.

He said he was not concerned by the Liberal decision to run a candidate against him.

“I’m not really focused about what the city parties are doing, I’m focused about running our race,” he said.

The Coalition party agreement in Victoria means the Liberals would not normally run a candidate against the Nationals in an election, but it is permitted in a by-election.

Liberal Party candidate Scott Rossetti is a prominent funeral director and local government figure, who has served three terms as Mayor of the Wellington Shire.

The Labor Party is a notable absence in the race, after deciding not to field a candidate.

Early voting for the by-election has opened and the polls close at 6pm on Saturday.

There are eight candidates in total on the ballot, including four independents and a Liberal Democrat.

-ABC