Deputy Premier Roger Cook has emerged as Mark McGowan's most likely successor with Transport Minister Rita Saffioti as his deputy, following the shock resignation of the popular WA premier yesterday.
Health Minister Amber-Jade Sanderson earlier won the support of MPs aligned to a key union, and remains in the race but will have to defeat the combined force of Mr Cook and Ms Saffioti, who late this afternoon announced they were forming a joint ticket.
Unless either Mr Cook or Ms Sanderson withdraws from the race, a five-week ballot process will take place, with Mr Cook acting as premier during that time.
"Late this afternoon I met with Roger Cook to confirm I would support his candidacy to be the next premier of Western Australia and would accept the role of deputy premier in any government he formed," Ms Saffioti said in a statement late today.
"The deputy premier and I have been parliamentary colleagues for 15 years, and cabinet colleagues for six years, and what we offer above all else is stable leadership – which is what our state needs right now.
"The deputy premier and I will continue to engage with our parliamentary colleagues as we seek to deliver unified and stable leadership for the state, and a consensus ticket for the party."
AMWU backs Cook
The left-aligned Australian Manufacturing Workers Union [AMWU] earlier said it would back Mr Cook as the party's new leader, with 17 WA MPs emerging from a special union meeting this afternoon to express their support for the deputy premier.
Their decision has split the left faction of the party, after the United Workers Union [UWU], which is also on the left, backed Ms Sanderson at a meeting this morning.
Emergency Services Minister Stephen Dawson, flanked by Arts Minister David Templeman, said the AMWU would support Mr Cook as premier.
"We've made a decision about what we think is best for Western Australia," Mr Dawson said.
"So our support is for Roger Cook as premier.
"Roger has been part of the leadership team for a long time and certainly one of our strengths as a government is how we dealt with COVID-19.
"Roger of course was a big part of that work, I think the community recognises and knows Roger and our team think he would be the best person to lead us moving forward."
The decision of the group was unanimous.
Sanderson claims majority support
Earlier, Ms Sanderson had said she had the "clear majority" support of her factional colleagues as the candidate to take over the party leadership.
"I will now reach out to my colleagues, with a focus on unity and stability," she said.
"We will continue those conversations, I will respect the process.".
The left faction holds power over the "progressive Labor" or right faction, and those who are unaligned in the middle.
Sanderson will do 'great job': MP
One of the MPs at the UWU meeting, Dave Kelly, spoke briefly after Ms Sanderson.
"She'll do a great job. I've got huge respect for Roger. We'll just move forward with the process," he said.
Rules introduced at a state level mean if two or more people nominate for the top job, a lengthy process would commence, requiring a vote of all the party's rank-and-file members.
The main thing the party would like to avoid is a drawn-out leadership ballot, something that could take up to five weeks.
The key to avoiding that is settling on a replacement quickly.
Parliament is due to sit in a fortnight and some MPs would prefer a consensus candidate to enable a smooth transition from Mr McGowan's leadership.
I have what it takes, Cook says
Ahead of the morning meeting, Mr Cook said he believed he had what it took to unite WA Labor and to become the next premier.
"I think it would be best if we could find a consensus candidate, someone who can unite the party, someone that the community recognises has a track record, and someone who would resonate with the community," he told ABC Radio Perth.
"That's why I've put my name forward and I think I can do those things.
"But I appreciate other people want to put their qualifications before the process."
When questioned whether he would go to a ballot if the left faction decided on Ms Sanderson today, Mr Cook reiterated his preference for a unanimous decision.
"We'll continue to have that conversation today, respecting the party processes, and make sure that we move through in a respectful manner," he said.
"I think it's important that we maintain the momentum that we've built up under Premier McGowan, and I'm very much looking forward to discussing with my colleagues the importance of maintaining that momentum."
Challenge for new premier: Gallop
Former WA premier Geoff Gallop said Mr McGowan's successor had big shoes to fill, but was confident about the party's future prospects.
"There's a lot of potential leaders in there so I'm pretty confident what will come out at the other end of the process will [ensure] good government continuing for WA," he said.
"Factions do play a part in Labor politics, Mark McGowan of course overcame that problem.
"He was seen very much as a person who was above the factions, so that's the challenge.
"What's important is that the person that gets the job then goes beyond that to make sure that he or she is governing in the interest of all West Australians."