Parts of Perth's biggest hospital will have to be temporarily shut while important fire upgrades are conducted, potentially putting extra strain on a health system already being stretched to record levels.

Health Minister Roger Cook said some wards would close while potentially dangerous cladding is replaced at Fiona Stanley Hospital.

That work is yet to be conducted years after the problem was first identified, sparking questions from the Opposition.

A review of WA health buildings with aluminium composite cladding was ordered after the disastrous Grenfell Tower fire in London in 2017, with Fiona Stanley Hospital (FSH) one of several facilities identified as needing work.

Mr Cook admitted work on panels at FSH was yet to be scheduled.

"The actual works, when they are [being] completed at Fiona Stanley Hospital, will require us to close down some wards," Mr Cook said in response to a question from WA Liberal leader David Honey in Parliament.

"That's obviously a very difficult piece of work and that's work which is going on right across all government assets to make sure that we can mitigate against the impacts of these aluminium composite panels (ACPs)."

'Situation under control', government says

Mr Cook said steps had already been taken to make Fiona Stanley safer, pointing to an enhanced fire system, an audit of fire walls and doors, a review of evacuation procedures, and extra fire training.

All smoke systems and sprinklers had also been reviewed, Mr Cook said.

But he said he wanted to see the work completed soon.

"We want to get on to Fiona Stanley Hospital as quickly as possible," he said.

"It's complex work which is the reason why to date they're focused on remediation, particularly on the entrances and exits of the building.

"It's a situation which is under control and is being worked through as a matter of course."

WA's hospitals already stretched

The looming closure of parts of FSH would potentially increase strain on WA's health system, which has been facing significant pressure.

Ambulance ramping has increased dramatically in WA over recent months, with paramedics stuck outside hospitals for more than 6,000 hours in August alone.

That figure shattered previous records.

Health authorities have also been forced to cancel scores of non-urgent elective surgeries, in a bid to ease pressure on the system.

That move has sparked fears from the Opposition and the Australian Medical Association that WA would not cope with a COVID-19 outbreak.

Several hospitals still require work

Mr Cook told Parliament that as of July, the vast majority of sites in the health sector identified by the aluminium composite audit — 85 out of 97 — were classified as not requiring further action.

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Remediation, planning and assessment for the remaining 12 was continuing, he said.

Assets had been classified from extreme risk to the lowest of risk.

"King Edward Memorial Hospital, for members' information, was identified as a high priority project which has already been completed," Mr Cook said.

"Royal Perth Hospital's program was completed in March 2021, Rockingham is to be completed by December 2021, and St John of God Midland health campus will be completed by November 2021.

"Obviously this is a very large project."

Cook blames former government

Small amounts of low risk ACPs and polycarbonate had been identified at Busselton Health Campus, Narrogin Hospital, Onslow Hospital and Warren Hospital.

After being asked by Liberal Leader David Honey why it had taken so long for FSH to be addressed, Mr Cook said the McGowan government had not built it.

"It wasn't us that built Fiona Stanley Hospital, we funded it, of course," he said.

"So perhaps you need to go back to the dodgy builder, which was the Liberal Barnett government."