With 50 per cent of the vote counted on Saturday night, One Nation was polling just 4.4 per cent of the vote in the WA lower house - far lower than expected.

A Newspoll at the start of February showed One Nation receiving 13 per cent of the vote.

Labor, led by Mark McGowan, will form government with a landslide victory and could win up to 40 seats - 10 more than required to form government.

Ms Hanson said she would carefully consider any future preference deals with the major parties following the result.

"It was a mistake," Ms Hanson said of the preference deal with the Liberal Party.

"I wasn't here to shore up [Liberal Premier] Colin Barnett but a lot of people do not understand the preference system."

Ms Hanson said she was still hopeful of winning seats in the WA upper house, which is only in the only stages of counting.

With four per cent of the upper vote counted, One Nation was polling fourth behind Labor, the Liberals and the Nationals but above the Greens.

Ms Hanson said the preference deal with Mr Barnett - whom she compared to "stale milk" the voters wanted to throw out - had suppressed her party's vote.

She said the One Nation executive would conduct a review of the campaign and how the party should allocate its preferences in the future.

Ms Hanson said the One Nation campaign was "rushed" and some disgruntled candidates had caused "havoc" during the campaign.

But she said the party had done "extremely well" to run candidates in most seats given in had little presence in WA before Christmas.

In some seats, One Nation was polling above the Nationals and Greens, she said.

"All in all I think we have done an excellent job," she said.

Premier Barnett said he was personally uncomfortable with the deal, but he understood the pragmatic reason it was made.

ABC journalists and camera operators were banned from attending the One Nation election event. Other media outlets, including Fairfax Media, were allowed to enter.