Counting from Saturday's by-election is continuing, with a projected swing of about 29 per cent against the government, spelling a historic loss for the Liberal Party.

Independent Joe McGirr has emerged as the favourite to wrestle the seat from the Liberals for the first time in more than 60 years.

The result is yet to be called, but the NSW government is already pouring over the entrails of the almost certain loss.

Ms Berejiklian took responsibility for the poor result, but then described the federal leadership coup, combined with the local corruption scandal that sparked the early poll, as "the perfect storm".

"The timing of the by-election, which coincided with other major events, other major political events, could not have been foreseen," Ms Berejiklian told reporters in Sydney on Sunday.

Labor leader Luke Foley criticised Ms Berejiklian for attempting to shift some of the blame to her federal colleagues.

"It's a bit rich to say 'I accept responsibility but it was my federal colleagues' fault' in the same breath," Mr Foley told reporters in Wagga.

"For the final count to be between Labor and an independent after six decades of entrenched Liberal representation, that's an electoral earthquake here in Wagga and Ms Berejiklian needs to hear the message."

Ms Berejiklian did apologise to voters for the by-election, forced by the resignation of disgraced MP Daryl Maguire amid a corruption inquiry.

"I want the people of Wagga to know that my government will work hard across NSW but especially in that region, to win back the trust that we have clearly lost."

She expects Dr McGirr to take out the seat.

"It's likely that we'll get the highest primary vote, but, of course, not enough to hold the seat. It's the most likely outcome, is that Independent Joe McGirr will win the seat," she said.

Dr McGirr said he was still coming to terms with the vote, saying he was "quietly optimistic".

He also ruled out joining any major party whether he was elected or not.

"I am an independent and I intend to continue as an independent ... even if I didn't get in," he told reporters.

Deputy Liberal leader Josh Frydenberg blamed local factors for the loss, but conceded "what happened in Canberra doesn't help the overall situation.

"But if you're looking for cause and effect, it was local factors," he told ABC TV on Sunday.

A Liberal loss leaves the door ajar for the NSW Nationals to run a candidate in the seat in the state election, with party leader John Barilaro having already confirmed his intention to run if the Liberals lost.

Australian Associated Press