A preference deal struck with the Liberal Party head of the West Australian election has ended up hurting One Nation, the party's leader Pauline Hanson says.

Ms Hanson joined One Nation supporters at a polling booth in Baldivis in Perth's southern suburbs on election day, handing out how-to-vote cards to voters.

Earlier, a Newspoll published in The Australian newspaper showed a marked drop in support for One Nation, which peaked at 13 per cent at the start of February but dropped to 8 per cent in the wake of the preference deal with the Liberals and ongoing problems with candidates.

The Liberals agreed to preference One Nation ahead of the Nationals in Upper House regional areas in the state, in return for One Nation preferencing the Liberals over Labor in all Lower House seats it contested.

Today Ms Hanson conceded the deal had not helped her party.

"I think it's actually done One Nation some damage," she said.

"It's been the biggest topic, people ask me about preferences and they don't understand the voting system, the preference system, the preferences. I'd like it to be introduced into the educational system.

"I think that's where most of the damage has come from."

Federal Opposition Leader Bill Shorten, who joined WA Labor leader Mark McGowan in the northern Perth suburb of Yokine, took aim at the Liberals over the agreement with One Nation.

Mr Shorten said Prime Minister Malcolm Turnbull should have condemned the deal.

"The Liberal deal with One Nation's been the ultimate exploding cigar of this election," he said.

"It just clearly shows a vote for One Nation is a vote for [Premier] Colin Barnett and the Liberal Party.

"And I have to say I think Malcolm Turnbull has been too weak in not stopping it."

Mr Barnett earlier refused to answer questions about One Nation after casting his vote in his electorate of Cottesloe.

"Not talking about One Nation, this is about the Liberal Party today," he said.

"I'm here to vote ... I don't really care too much about Pauline Hanson and One Nation. My opponent is the Labor Party."