Dozens of hospital patients were “dragged outside in their beds and on mattresses” when a fire broke out near an accident and emergency unit.
A major incident was declared at the Royal Stoke University Hospital at about 18:00 BST.
Six fire engines were sent to the scene, Staffordshire Fire and Rescue Service said.
Pictures show evacuated patients, hospital staff and visitors congregating outside the hospital.
University Hospitals of North Midlands NHS Trust said the fire was in the main building, which now needs to be ventilated.
Eyewitness Paul Bradbury had gone to visit his mother in critical care but was told he could not go inside because there had been a fire in a theatre and smoke was coming into a corridor. He saw fire engines arrive about 10 minutes later.
“People were then dragged outside in their beds and on mattresses. It was quite surreal to see really,” he said.
“The staff worked incredibly well in getting everybody out.
“There were quite a few nervous patients, but lots of nurses were with them and they were happy to be out and seemed fairly relaxed. There was no panic. It was very well managed.”
Patients were being allowed back inside from about 20:15.
People are being asked to stay away from A&E until Thursday and use Haywood Hospital instead.
A hospital spokesman said: “The priority is now to ventilate all the wards affected so patients can be safely returned. We would like to thank all patients, relatives and members of the public for their patience and understanding during this major incident.”
West Midlands Ambulance Service said it had a number of staff at the hospital who assisted during the incident.