There are big job cuts on the way in Western Australia's health system as federal funding dries up.

The WA Health Department has been forced to reduce costs to match reduced national funding levels over the next eight months.

Money for WA hospitals is based on national and state formulas linked to their “activity level” – time spent treating patients.

But due to a combination of higher wages and lower efficiency, WA hospitals have been granted the equivalent of more staff per patient compared to other Australian hospitals.

WA Health Minister Kim Hames says it has to change.

“We know that they're over-budget. We know they're well in excess of staff numbers. But they need to work it out, division by division, working out how they can save FTEs [full-time equivalents],” he told Parliament.

Dr Hames said hospitals could find ways to reduce costs without sacking staff.

“They can do a whole range of things. Changing on-call rates, changing overtime rates, changing the range of things to make sure they can retain those FTEs.”

But Opposition Leader Mark McGowan slammed the move to cut costs at a time when pressure on hospitals was increasing.

“At a time when outpatients [departments] are under pressure, emergency departments are under pressure, surgery waiting lists are under pressure, it appears the Government will be sacking hundreds, if not up to 2,000 people, West Australian health workers,” he said.

“That includes nurses, doctors, assistants and the like in our hospitals.”

Opposition Health spokesman Roger Cook said the toll could be over 1,000 jobs.

“We've heard that at least 500 people will be sacked from Royal Perth Hospital, at least 600 from Fiona Stanley Hospital,” he told Parliament.

“What's clear is the Barnett Government have completely stuffed up the state's finances and it's WA patients that are going to have to pay the price.”

Dr Hames said he could not predict the final number of job losses.

“So we won't know how many FTEs are lost. What we know is the budget that they have to mitigate for,” he said.

Dr Hames said staff would be sacked progressively over coming months, with the total amount becoming clear by mid-2016.