One Nation wins first lower house seat in WA after Secret Harbour by-election

One Nation leader Pauline Hanson has thanked Western Australia's Liberal leader Basil Zempilas for directing votes to her party at the weekend's Secret Harbour by-election, calling him a "man of vision and common sense".

Luke Herdegen easily won the by-election in the outer-suburban seat, previously held by Labor for almost 20 years, giving One Nation its first parliamentary seat in WA's lower house.

The Liberals had preferenced One Nation third on their how-to-vote card after the Australian Christians.

"I'm so grateful to Basil," Senator Hanson told 102.5 ABC Perth when asked about the Liberal preferences.

WA One Nation leader Rod Caddies said his party and the Liberals had the same goal.

"They may not have won the election, but they do have a common goal of getting rid of a Labor government," Mr Caddies told 102.5 ABC Perth.

Mr Zempilas has acknowledged the Liberal preferences helped One Nation win Secret Harbour.

But he again denied the Liberals had run dead in the campaign, as suggested by federal Liberal MP Andrew Hastie, whose seat of Canning overlaps Secret Harbour and who will be vulnerable to One Nation's growth at the next federal election.

Mr Zempilas, however, did maintain the Liberals could do better.

"Seventeen per cent [the Liberals' vote at the Secret Harbour by-election] is not at the numbers that we would want it to be at," he told 102.5 ABC Perth.

"But we are very, very mindful that this is a by-election in a seat that we have never held and never done well in.

Cook decries Herdegen 'hubris'

Mr Herdegen won the by-election with just over 57 per cent of the two-party preferred vote compared to almost 43 per cent for Labor candidate Georgia Tree, after 74.5 per cent of ballots were counted.

He told 102.5 ABC Perth today that his populist party had now set its sights on forming government at the 2029 state election, banking on what he called the beginnings of a "huge shift" in voters in this Labor stronghold.

"I think people are making smarter decisions now on who they do vote for," Mr Herdegen said.

"We've seen the beginning now of a huge shift, and I expect that momentum to keep going.

His claims were quickly shot down by Premier Roger Cook as "arrogance" and "hubris".

"That's the sort of arrogance that trips you up in this game," Mr Cook said.

"Hubris is usually served up with a double helping of humble pie when you go around with that sort of attitude."

Mr Cook said Labor treated the community with respect and never took voters for granted.

"There's no complacency in my team. None at all," he said.

'Wake-up call'

But South Australian Labor premier Peter Malinauskas said it was time for his party to "wake up".

"There is a movement here that has got momentum and we've got to make sure we're doing the right thing by whoever it is you're representing, in whatever state or whatever level of government," he said.

"You've got to have a policy conviction and get on and do things, otherwise people will mark you down for it."

Labor still dominates WA's Legislative Assembly, known as the lower house, with 45 seats. The Liberals hold seven seats, the Nationals six and One Nation now one.