WA Treasurer Troy Buswell has resigned from Cabinet following what Premier Colin Barnett described as a "breakdown".

It follows reports he was involved in a car crash before taking personal leave more than two weeks ago.

At the time Mr Barnett explained the leave by saying Mr Buswell had taken time off for health-related reasons.

However on Monday morning Mr Barnett called a press conference to say Mr Buswell had called him on Sunday afternoon to tender his resignation.

Mr Barnett also outlined the chain of events stemming from a crash involving Mr Buswell's ministerial car on February 23.

He said Mr Buswell's chief of staff, Rachael Turnseck, had alerted him to Mr Buswell's health condition the following day but he had not been aware of the crash at that time.

Sorry, this video has expired Questions over who knew of Buswell crash ( Andrew O'Connor )

"She advised me that Troy had had a breakdown, was not in good shape, very emotional, very upset, and that he was in medical care," Mr Barnett said.

"She also advised me that Troy had requested privacy, and I think that's the view of those close to him, that he needed that privacy.

"He was going on leave, quite appropriately described as personal leave, and I called on people to respect his request for privacy.

"Therefore, I did not inform Cabinet, nor the Liberal party room, of what I knew of his health condition."

Mr Barnett says Mr Buswell has since been treated in hospital in Perth and a clinic in Sydney.

He has now been released but is still receiving medical treatment.

No recollection of crash

Mr Buswell's ministerial car was involved in a crash outside his home in Subiaco in the early hours of February 23.

Police Commissioner Karl O'Callaghan confirmed police received a call just after 1:30am about a vehicle being driven erratically on Roberts Road.

He said two officers from the traffic enforcement unit were despatched to a 317, the code for an alleged drink driver.

When two constables arrived at the address, they noted the vehicle that had been reported was locked behind a gate and was damaged.

The damaged front bumper of Treasurer Troy Buswell's car. ( ABC News: Graeme Powell )

"They had no information about who the driver was, they had no information about who the vehicle might have been in possession of, and they had no information about the premises they were going to that would have linked the premises to Mr Buswell," Mr O'Callaghan said.

However, he says the person who reported the erratic driver does say almost six minutes into the call "we actually joked between ourselves that we thought it looked like Troy Buswell".

"Now they could have said it looked like Meryl Streep or anybody else," Mr O'Callaghan said.

"That doesn't give the CAD operator anything to go on. And the operator then said, 'Can you give me further information about what he was wearing?' It was clearly put in a context of a joke because he said: 'We joked'."

Mr O'Callaghan said it was impossible to identify the vehicle was being driven by Mr Buswell as it was registered to the Office of State Administration.

"So I'm not sure because I haven't spoken to the officers concerned yet what inquiries they made that night," he said.

"But I can tell you they would not have been able to get any details of a vehicle that's registered to the Office of State Administration in terms of who it's normally in possession of."

Mr Buswell's vehicle is still sitting in the carport with its front bumper on the driveway.

Premier says he had no knowledge of crash

Mr Barnett said he was not informed about the crash until Sunday afternoon.

"I became aware of that at about 2pm yesterday," he said.

"I was aware that there had been information supplied to the police of erratic driving, and also that there was some damage to the vehicle."

Mr Barnett says Mr Buswell could not shed further light on the incident.

"He said he basically didn't have much recollection," he said.

Sorry, this video has expired Troy Buswell's career marked by misadventure ( Charlotte Hamlyn )

"Not denying anything at all, making no excuses and could offer no reasonable explanation for what had happened.

"Again, he's very emotional, very upset, very apologetic."

Opposition Leader Mark McGowan says he is suspicious of claims no-one in the Government knew about Mr Buswell's car accident before Sunday.

"I just find it all amazing, and inexplicable, and I think there is a cloud of doubt that hangs around these things," he said.

"I think therefore all of the information that the police have, and the ministers, staff in all of those offices, needs to be released.

"I've been in Parliament for 17 years and I've seen a lot of things. Generally people are talking about these sorts of things. Generally there is knowledge, and I find it amazing if there are claims that no-one knew."

Buswell's controversial career

Key moments in Buswell's career February 26, 2005: Elected to represent the seat of Vasse.

February 26, 2005: Elected to represent the seat of Vasse. January 17, 2008: Assumes leadership of the WA Liberal Party. Accused of snapping the bra strap of a female Labor staffer, and also admitted making a sexist remark to a fellow MP.

January 17, 2008: Assumes leadership of the WA Liberal Party. Accused of snapping the bra strap of a female Labor staffer, and also admitted making a sexist remark to a fellow MP. April 29, 2008: Tearfully acknowledges sniffing the chair of a female staffer in late 2005.

April 29, 2008: Tearfully acknowledges sniffing the chair of a female staffer in late 2005. August 4, 2008: Resigns as Opposition Leader in the "best interests of the party" one month before state election.

August 4, 2008: Resigns as Opposition Leader in the "best interests of the party" one month before state election. September 6, 2008: Liberals defeat incumbent Labor party at election.

September 6, 2008: Liberals defeat incumbent Labor party at election. September 23, 2008: Appointed to Cabinet as Treasurer, Minister for Commerce, Science and Innovation, Housing and Works.

September 23, 2008: Appointed to Cabinet as Treasurer, Minister for Commerce, Science and Innovation, Housing and Works. April 27, 2010: Steps down after allegations he used public funds to arrange meetings with lover and then Greens MP Adele Carles. However, both were later cleared.

April 27, 2010: Steps down after allegations he used public funds to arrange meetings with lover and then Greens MP Adele Carles. However, both were later cleared. December 14, 2010: Elevated back to Cabinet as Minister for Transport, Housing, and in July 2012 regains Treasury portfolio

December 14, 2010: Elevated back to Cabinet as Minister for Transport, Housing, and in July 2012 regains Treasury portfolio February 8, 2014: Settles defamation case against former partner Adele Carles.

February 8, 2014: Settles defamation case against former partner Adele Carles. March 10, 2014: Resigns from Cabinet after what Premier Colin Barnett describes as a "breakdown" amid reports he was involved in a car crash before taking personal leave.

Mr Buswell's career in politics has been marred by indiscretions.

He was forced to resign as the leader of the WA Liberal Party in 2008 after admitting he sniffed the chair of a female staff member and snapped a Labor staffer's bra.

Mr Buswell was then appointed to the front bench under Mr Barnett.

He then stepped down as treasurer in 2010 after allegations surfaced that he used public funds to arrange meetings with lover and then Greens MP Adele Carles.

Mr Buswell and Ms Carles were both cleared of misusing ministerial entitlements in June 2010 and Mr Buswell returned to the front bench in December.

He was advised by the Premier when appointed treasurer that he was on his final warning.

Last year, Mr Buswell denied trying to hide a controversial budget decision involving the WA Insurance Commission, which allowed the Government to take up to 65 per cent of the commission's profits.

The Premier has assumed temporary responsibility of the Treasury and Transport portfolios, and will be assisted with the budget process by Finance Minister Mike Nahan.

He said he planned to keep portfolio changes to a minimum but there would be a new appointment to Cabinet.

Mr Barnett said he hoped to announce any ministerial changes by the end of the week.