Doctors say the latest report card on public hospitals shows the system is overstretched and running about 400 beds short with no improvement over six months.

The Health Department's quarterly health performance report to March shows virtually no increase in overnight and day beds in Perth's public hospitals, with 3537 available beds — only 13 more than in September.

The occupancy rate of beds was almost 86 per cent in March, up on the 84 per cent rate six months earlier.

The Australian Medical Association WA estimated that public hospitals needed at least another 400 beds and said the latest figures suggested numbers had stayed virtually static since midway last year.

Spokesman Professor Geoff Dobb said hospitals were forced to work harder with a fixed number of beds. "What this means is that there's little spare capacity and little scope to reduce average length of stay so that means bed occupancy is rising and gives lie to the Treasury assertion that WA doesn't need additional bed capacity," he said.

"Given the trends demonstrated by these figures, we're going to have find the money from somewhere because if we were to have additional stress such as a normal winter flu outbreak then that's really going to compound the problem."

Shadow health minister Roger Cook said more beds were supposedly going into Rockingham Hospital but there was no sign it was boosting overall numbers.

"It's concerning that the Government is failing to build capacity in the system, despite having a lot of new infrastructure which is coming onstream," he said.

But Health Minister Kim Hames said the Government was working hard to boost bed numbers and employ the staff to keep them open.

He said hospitals were running at close to capacity and more progress would be made under the new fourhour rule that aimed to streamline movements in emergency departments and wards.

CATHY O'LEARY MEDICAL EDITOR