Former One Nation politician Pauline Hanson has a good chance of winning the final NSW upper house seat.

Ms Hanson is 6000 votes ahead of her nearest rival, the Greens' Jeremy Buckingham, with 91 per cent of primary votes counted, ABC election analyst Antony Green said.

The full result is expected to be declared tomorrow, more than two weeks after the state election on March 26.

So far 20 of the 21 upper house seats up for election have been filled, with the Coalition winning 11 of the vacancies.

Labor has won five of the seats, the Greens have two, and the Shooters and Christian Democrats each have one.

Ms Hanson is standing as an independent candidate, having severed formal links with One Nation, the party she co-founded.

She moved to the NSW central coast last year and announced last month she intended to run for an upper house seat.

Pauline Hanson in line to win NSW upper house seat