The Greens appear likely to win four seats in the New South Wales Lower House after polling strongly in inner Sydney and on the state's north coast.

The party had just one MP in the Lower House before the election: Jamie Parker in the inner-Sydney seat of Balmain.

Mr Parker is expected to hold on to the seat with an increased majority, and Greens candidate Jenny Leong has claimed victory in the neighbouring seat of Newtown.

ABC election analyst Antony Green said the party was also likely to seize the seats of Ballina and Lismore from the National Party, after coal seam gas (CSG) became a key election issue on the north coast.

The Nationals had held both seats with margins of more than 20 per cent.

"We've got a preference count that would give [Ballina] to the Labor Party, but the Labor Party's going to finish third so I suspect that will be a Green victory in Ballina," Green said.

Lismore was also likely to fall to the Greens after the National Party's primary vote dropped below 40 per cent, he said.

"With Labor and the Greens with 55 [per cent] between them, I'm expecting ... Adam Guise will be the new Green member there," Green said.

Mr Guise was cautious about claiming victory prematurely but said the party had changed the political landscape on the state's north coast forever.

"There's a clear vote against coal seam gas across the region," Mr Guise said.

"There's a clear message that the old parties have to listen to our electorate, and actually end the corruption in the parties and get on with the job of rolling out renewables."

The Nationals' candidate for Ballina, Kris Beavis, said the retirement of incumbent Nationals MP Don Page took the seat of Lismore "back to a 50-50 proposition".

He said CSG had been of major concern to voters.

"What I saw when I was out doorknocking and meeting people in the street is there's probably 80 to 90 per cent of people [who] do have a concern with CSG," Mr Beavis told Channel Seven.

Ballina's new Greens MP, Tamara Smith, said the win was difficult to believe.

"It's so startling to have gone from a safe Nationals seat for 27 years to the Greens," she said.

"I think it just sends an incredibly loud message that people are ready to deal with climate change, renewable energy and they don't want coal seam gas in this area."

Upper House Greens MP John Kaye said he was not surprised the party had done well on the north coast.

"[We have] really strong policies for two hot button issues - TAFE and coal seam gas," he said.

"The community knew we'd been campaigning on those issues for a long time."

In the newly created seat of Newtown, Ms Leong defeated Labor frontbencher Penny Sharpe, who has served in the Upper House since 2005.

Ms Leong said the victory gave Newtown an opportunity to "reshape the progressive agenda in New South Wales".

"The Greens have a long and strong tradition of standing with the community, having strong voices in Parliament but also on the streets," she said.

"And can I say that what this win in Newtown means tonight is that there will be no WestConnex [motorway] coming into Newtown."

Liberal deputy leader Gladys Berejiklian said the Greens had capitalised on Labor's negativity.

"This campaign, in all fairness, the Labor Party has talked about what they don't support," she said.

"They haven't really talked much about what they do support.

"I think that's caused a lot of people to go to the Greens, and that could be a trend that continues into the future."

Federal Labor senator Deborah O'Neill said the Greens' success in taking country seats from the National Party represented a big change for NSW.

"But this does reflect, in some ways, the movement that we've been seeing on a federal level for some time," she said.

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