New South Wales Deputy Premier Troy Grant will face a leadership spill on Tuesday, with Nationals MP Andrew Fraser saying he will put up a motion after a massive backlash against the Nationals in the Orange by-election.

With more than 50 per cent of the vote counted, the Nationals managed to keep around 30 per cent of first preference votes, while just under 25 per cent went to the Shooters Fishers and Farmers' Phil Donato.

The Nationals hold Orange by a 21.7 per cent margin, and it has not changed hands since 1947.

The seat became vacant when former MP Andrew Gee resigned to run for Federal Parliament earlier this year.

The Nationals candidate in Orange, Scott Barrett, is a former ABC reporter who later worked for Bob Katter and in recent years has been a policy adviser to the Baird Government.

But voters angry at council amalgamations and the now scrapped greyhound racing ban abandoned the party in bigger than expected numbers.

"There has to be a leadership spill," said Mr Fraser.

"There are three things that gave us such a poor result in Orange. Number one was leadership, number two was greyhounds and number three was councils."

Mr Fraser will put up the motion at the first party room meeting on Tuesday.

Troy Grant declined to comment and said in a statement that the result in Orange is still not clear.

Philip Donato might take the NSW seat of Orange off the Nationals for the first time since 1947. ( ABC News: Joanna Woodburn )

Shooters party candidate Phillip Donato, who campaigned strongly against the greyhound ban, said his strong showing in the counting so far was "very encouraging", but there was a long way to go yet.

"It sends a strong message to the Government that you need to listen to your constituents," Mr Donato said.

"You can't make these decisions without consultation."

He said the greyhound ban and the forced council amalgamations were issues that resonated really strongly in the area.

"Voters are really angry at the Government and the party that they've been loyal to for nearly 70 years," he said.

Nationals 'very poorly positioned'

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ABC election analyst Antony Green said it would be tough for the Nationals to win, and preferences may push the Shooters over the line.

"It looks like the Nationals are very poorly positioned in their hope to hold the seat," he said.

"It's a huge swing … at the end of the night they're only 5 per cent ahead on [first] preferences.

"Most of the other candidates on the Ballot paper directed preferences against the Nationals.

"The Labor party all directed preferences against the Nationals so you'd estimate they'd be really lucky to hold the seat."

The remaining pre-poll, postal and second preference count got underway on Sunday and it could be days before a final result is known.

The electorate has not changed hands since the end of World War II, and its margin was one of the state's biggest.

A loss could spell the end of Mr Grant's leadership, amid criticism he is not representing the views of country voters to the state's Premier Mike Baird.

Voters angry at council amalgamations and the greyhound ban abandoned the Nationals Party. ( Facebook: Philip Donato )

Labor holds Canterbury and Wollongong

Meanwhile, Labor will retain the seats of Canterbury and Wollongong, which also held by-elections on Saturday.

In Canterbury, former Upper House MP Sophie Cotsis is on track to increase the party's margin by more than 15 per cent.

With about 70 per cent of the vote counted, she led on the two-party preferred vote by 77.9 per cent to her nearest rival, Christian Democrats Branka Kouroushis, on 22.1 per cent.

In Wollongong, Labor's Paul Scully had managed a first-preference swing of 7.9 per cent towards his party with about 80 per cent of the vote counted.

Labor Party figures had been concerned that independent candidate and Lord Mayor of Wollongong, Gordon Bradbury, would present a challenge to their hold on the seat, but while he managed almost 34 per cent of first preference votes it was not enough.

The Liberal party did not run a candidate in either seat.