The SFF candidate Philip Donato​ hoped preferences distributed from the Labor party would be enough for him to eventually overcome the Nationals 69-year hold on the seat.

"We are a real alternative to the National party," Mr Donato, a police prosecutor, said on Sunday. Whatever the result, he said "the message to Macquarie Street is clear: Orange deserves better."

The Nationals held the seat on a 21 per cent margin going into the election but candidate Scott Barrett was only slightly ahead in the primary vote as counting continued on Sunday. Some booths recorded swings of more than 60 per cent.

Mr Grant, the Deputy Premier, faced the prospect of a leadership spill as veteran Nationals MP Andrew Fraser confirmed on Sunday he would call for a vote. "He should just walk away," Mr Fraser said.

Robert Borsak, an SFF member of the NSW upper house, said his party's showing in Orange put the Coalition on notice for the next state election.

"This is win for the deplorables," Mr Borsak said, referencing Hillary Clinton's description of Donald Trump voters.

"We are going to campaign very hard across the board in 2019 ... unless the government pulls up its socks, it's really up to them whether the government will change."

Mr Borsak said the Nationals had been largely invisible in the last week of a campaign dominated by issues such as forced council amalgamations and the now-reversed ban on greyhound racing.

Mr Donato said disenchanted voters doubted the "integrity" of the decision to reverse the ban.

Orange garbage collector Bruce Johnson, 58, said he had voted National all his life but switched to the SFF on Saturday.

"This is a big protest vote," Mr Johnson said, singling out greyhounds and amalgamations as the biggest factors, while describing Mr Donato as decent and honest.

Ross Maroney, a retired school teacher, said "there was an awful lot of feeling and blame towards the Nationals" on the greyhounds issue.

On amalgamations, Mr Maroney, 73, said parts of the electorate felt they were already paying exorbitant rates and now risked missing out on services. "The people around here in the surrounding villages are terrified," he said.

Sydney radio presenters Alan Jones and Ray Hadley travelled to the central-western city last week to urge voters to put the Nationals last.

Orange has been a Nationals seat since 1947. The byelection was called after sitting member Andrew Gee quit to successfully contest the seat of Calare at the federal election in July.