The vast majority of hospitals in England are struggling to recruit enough nurses, figures show.
Some 92% of the 225 acute hospital trusts in England did not manage to run wards with their planned number of nurses during the day in August.
The figures, published by the NHS, show that hospitals in England are falling short of their own targets for levels of safe staffing.
The Department of Health said staffing was a priority.
Analysis by the Health Service Journal shows average staffing levels across the 225 acute hospital sites in August was worse compared with data for January when 85% of hospitals missed their staffing targets for nurses working during the day.
The figures also showed 81% of hospitals failed to have enough registered nurses working at night.
Some 79% of hospitals missed their target for registered nurse staffing across both day and night.
Hospitals have been required to publish monthly data on whether they have enough nurses on wards since April 2014.
It followed a report into the Mid Staffordshire NHS Trust, which was heavily criticised for failings of care that may have contributed to unnecessary deaths.
Many hospitals have had to boost their nurse numbers by recruiting overseas, and spending on agency staff has contributed to NHS deficits.
The Department of Health acknowledged there were big challenges for hospitals and said staffing was a priority.