The Queen Elizabeth Hospital in Norfolk has promised to take swift action to improve its quality of care after being placed in special measures.
Following confirmation from the Care Quality Commission that the health regulator Monitor was to intervene, the King's Lynn trust apologised to patients.
Acting chief executive at the QEH, Sharon Beamish, said: "We accept the reports' findings and as a board we will work with Monitor to do everything we can to put things right as quickly as possible."
The hospital said it was taking immediate action to ensure wards were adequately staffed.
A further 35 nurses from Portugal are due to start work at the King's Lynn site in November and December and the trust is continuing to recruit from across the UK - including newly-qualified staff from the University of East Anglia and Anglia Ruskin University.
A Norfolk hospital has been placed in special measures after "consistently failing to meet the national standards of quality and safety", the Care Quality Commission (CQC) has confirmed.
The Queen Elizabeth Hospital, in King's Lynn, has been warned it must improve standards as quickly as possible.
It follows a request by the CQC to regulator Monitor to step in and place the Gayton Road hospital in special measures after it was found to be failing on "more than one occasion".
The QEH was issued with a formal following an inspection in August which found low staffing levels and a lack of training in connection with dementia care. Patients were also found to be at risk because systems in place were not robust enough.
It followed an earlier inspection in May when the hospital was also told to improve.
Sir Mike Richards, chief inspector of hospitals for the CQC, said: "The concerns we found ... were so great we felt it was necessary to request that Monitor intervene and place the trust into special measures to assist in driving through improvements for patient care."
The trust will be closely monitored by the watchdog to ensure standards are raised.