Patients were urged to stay away from two Southampton hospitals as a major incident was declared following a power cut.
Relatives were asked not to visit Southampton General and Princess Anne hospitals on Wednesday to allow staff to care for patients while power was being restored.
An electrical cable led to a fault which caused a power failure across the whole trust, the University of Southampton NHS Foundation Trust said.
Power has since been fully restored.
Patients were able to stay safe, the trust added in a statement, as vital equipment was able to stay on through battery back-ups.
A spokesman for University Hospital Southampton NHS Foundation Trust said all patients were safe but all non-urgent activity had been cancelled on Wednesday.
He said: "As the electrical cable fault which led to a power failure across the trust has been resolved, we have now resumed emergency and trauma surgery and power has been fully restored across Southampton General and the Princess Anne hospitals.
"Despite this affecting our emergency generator, we were able to keep our inpatients safe through battery back-up of vital equipment and their care remained unaffected throughout.
"However, as non-urgent operations and appointments scheduled for today were cancelled, some patients will now face delays in receiving their scheduled care with us but we aim to ensure they are rearranged as quickly as possible with prioritisation given based on clinical need.
"We would like to thank patients and relatives for their understanding and our partner organisations and neighbouring hospitals who provided excellent support to manage the increased pressures on our services.
"Above all we would like to say a special thanks to our staff who handled the situation calmly and with complete professionalism at all times to ensure our patients received the highest standards of care in difficult circumstances."
