Liberal backbencher Murray Cowper has confirmed he will call a leadership spill at Tuesday morning's partyroom meeting, in a bid to oust West Australian Premier Colin Barnett from his position.

Mr Cowper's decision will pit Mr Barnett in a leadership contest against his former Transport Minister Dean Nalder, who confirmed on Sunday he would seek the top job if a spill was moved.

Mr Cowper's move to initiate a spill follows the resignations of Mr Nalder and Local Government Minister Tony Simpson from Cabinet, and claims from former Mental Health Minister Helen Morton of "bullying and intimidation" emanating from the Premier's office.

Those four, along with Morley MP Ian Britza, have all publicly declared they no longer support the Premier.

Government 'bleeding out'

Mr Cowper said he advised Mr Barnett earlier on Monday that he would move a spill at Tuesday's party room meeting.

"At the moment we are simply bleeding out and if we don't stem the flow, what we are going to do is hand to the Labor Party by default the leadership of this state," the former Corrective Services Minister said.

"My actions are in line with his comments to the party room that he would graciously step aside if it was in the best interest of the party.

"It is clear to me that he has no intention of honouring this statement."

Mr Cowper pointed to the Government's management of January's devastating Yarloop bushfires as a reason for his loss of faith in the Premier, saying he attempted to contact Mr Barnett repeatedly and was unable to do so until dozens of homes had been destroyed.

It will be the first leadership contest in the eight years of the Barnett Government.

Earlier, Mr Barnett said he remained confident he had the numbers to defeat a spill motion and he felt "personally let down" by Mr Nalder.

"There has certainly been a lot of agitation about leadership and a lot of swirling of rumours and discussion around Parliament House and the like and I'm disappointed in that," he said.

Murray Cowper says he has lost faith in the Premier's leadership. ( ABC News: Andrew O'Connor )

"I think he's missed a great opportunity to make a big contribution to this state."

Mr Nalder outlined his case for the leadership in a series of media appearances across the day, saying the Premier had lost his way and the community had stopped listening to him.

"I am prepared to put my hand up because I don't believe the leader is focused on a way forward," Mr Nalder said.

"We are not there to finish a legacy."

Deputy Premier standing by Barnett

Earlier on Monday, Deputy Premier Liza Harvey led a group of remaining ministers in declaring "unequivocal support" for Mr Barnett as they arrived for their weekly cabinet meeting as a group.

"Should there be a call for a leadership spill in the party room tomorrow, we will not be supporting that," she said.

"From that party room tomorrow Colin Barnett will emerge as the leader of the Liberal Party, the Premier of Western Australia, and he is absolutely the right person to take us through to the election in March 2017."

Ms Harvey said she was "mortified" by the actions of Mr Nalder, Mr Simpson and Mr Britza, saying all three were linked to a group of business figures who commissioned a privately funded opinion poll showing the Government was headed towards electoral defeat.

Mr Nalder came close to being sacked from Cabinet after it was revealed he had received a copy of the poll results days before their public release but never informed the Premier.

Ms Harvey confirmed if there was a spill motion, she would not nominate for the leadership.