Addenbrooke's Hospital in Cambridge was temporarily forced to close its A&E department due to problems with its computer network.
The hospital declared a "major incident" for a short time on Monday afternoon.
As a result, people were urged to choose alternatives where possible so that staff could prioritise the sickest patients.
The issue has now been resolved but the trust which runs the hospital says A&E remains very busy.
"Cambridge University Hospitals can confirm computer network issues have now been resolved," a Cambridge University Hospitals (CUH) spokesperson said.
"However, patients are advised that our Accident and Emergency department is still extremely busy and as a consequence we remain in major incident.
"CUH would like to thank patients and staff for their support during this incident."