People being treated at the Bristol Royal Infirmary said they heard what some thought was an “explosion” and were told to leave the site immediately.
Multiple emergency services remain at the scene in Bristol city centre after what hospital bosses have since described as a “power outage”.
The hospital has said told BristolLive that there was no ‘roof collapse’ despite a number of employees being told this.
Lisa Davidson, 50, a housewife from Bristol, was having a blood infusion for Crohn’s disease.
She said: “All the lights went off and they kept flashing on and off.
“Then they told us to go out, we couldn’t find our way out. We tried to get out from the main entrance but that was locked so we had to come out from the car park.
“It was really scary, I felt a bit upset. They had to stop my infusions to evacuate. It was like a nightmare.”