Anaesthetised children who were about to have operations were among patients evacuated from Great Ormond Street hospital today after a fire and explosion.
The hospital's chief executive Dr Jane Collins said the incident, which is thought to have involved a gas cylinder, happened in the cardiac wing of the London children's hospital.
No-one was believed to have been injured.
Dr Collins told reporters: "There was a fire in our cardiac block this morning that seemed to have led to an explosion, probably that of a medical gas cylinder.
"We obviously put our major incident plan into action very quickly and evacuated all of the patients and staff from that block.
"As far as I know at the moment there have been no injuries to any patients, parents or staff member.
"This incident may mean our cardiac wing may have to remain closed for a while."
Dr Collins said that some patients would have to be transferred to hospitals nearby including the Brompton Hospital and Guys Hospital, particularly those needing urgent operations.
She said there were around 30 or 40 patients in the cardiac wing at the time of the fire.
Dr Collins added: "Depending on how ill the children were they were evacuated to the appropriate place, so a child who was particularly unstable would have been moved to our intensive paediatric unit very quickly.
"There were some children who were due to have surgery this morning so they were already in the process of being anaesthetised.
"We have already woken these patients up because we want to make sure they are in a stable and safe situation.
"We are very concerned about the potential damage to the cardiac wing and the damage it could do to our cardiac programme."
Cleaner Temitope Olowu, who was working on the fifth floor of the hospital when the fire broke out, said: "We were working away and we were suddenly told there was a fire on our floor, level five so we were all ordered to the nearest fire exit.
"We didn't really know what was happening.
"Everyone was keeping calm and just concentrating on getting out of the building.
"We were sent outside and told to stay there until further notice.
"We have all be gathered outside now for quite a long while."
Four firefighters suffered minor injuries while tackling the blaze at the specialist hospital near Russell Square, central London and were treated by paramedics at the scene.
A spokesman for London Fire Brigade said it was not yet clear what caused the explosion.
Six fire engines and about 30 firefighters were sent to the hospital just after 8.30am.
Day patients who arrived for treatment today were sent home, Dr Collins said.
Two ambulances and a hazardous area response team, which tackles sites with additional risk factors such as chemicals and gas canisters, were also sent to Great Ormond Street, the London Ambulance Service said.
Police were directing traffic around the site and, once the blaze is extinguished, will assist London Fire Brigade in investigating the cause, a Scotland Yard spokesman said.
Today's blaze followed a fire at the Royal Marsden Hospital in January, when dozens of patients were evacuated.
Flames tore through the roof and upper floors of the world-class specialist cancer hospital in Fulham Road, London.
Two wards and five operating theatres were damaged by the fire, and a number of patients were treated at the nearby Royal Brompton Hospital.
Great Ormond Street confirmed at 1pm that it was no longer planning to transfer patients to other hospitals.Reuse content