The Care Quality Commission has issued a formal warning to Avon and Wiltshire Mental Health Partnership over levels of staffing at Blackberry Hill Hospital in Bristol.
It followed an unannounced inspection of three wards at the Fromeside Unit in December. The medium secure unit provides specialist care and treatment for adults with mental disorders, which may mean that they are at significant risk of harming themselves or others.
Inspectors found that the unit was failing to comply with the national regulation on staffing and did not have not enough qualified, skilled or experienced staff to meet people's needs.
More top news
Alex Sims, 10, has a rare auto immune disease and without a transplant he will die.
Dante Bowlin was last seen in the Matson area of Gloucester two days ago.
Residents living within 100m of Reeco Fernandez's property were advised to leave their homes and had to stay away for five days.