It was part of the NHS's long-rehearsed emergency plan for dealing with disasters. Alerted by the police, hospitals across the capital cleared beds, cancelled operations and summoned staff to deal with the casualties.
Mobile medical teams were dispatched to stabilise the critically injured. At Aldgate East station, patients were treated on the pavement outside. A convoy of double-decker buses was used to ferry patients to the Royal London hospital, in Whitechapel, where nurses were stationed with trolleys and chairs.
The London Ambulance Service said it had dealt with 45 critically injured patients and 300 "walking wounded" suffering from burns, fractures, the effects of smoke inhalation and perforated ear drums - all injuries typical of the effects of an explosion. At least 1,000 people are thought to have been hurt.
Casualty clearing-stations were established close to the site of each incident. The Hilton Metropole Hotel, opposite Edgware Road station near Paddington, opened its doors spontaneously to dozens of victims.
The headquarters of the British Medical Association in Tavistock Square, where the bus exploded, was spattered with blood. Body parts were strewn across the road. Two people died in the courtyard of the building as doctors from the 120,000-member organisation tried to save them. BMA House was used as a casualty station before victims were taken to hospital.
Dr Laurence Buckman, from the BMA's GPs committee, said that doctors had worked alongside ambulance and other emergency staff to treat patients for shock, administer drips and stem bleeding. "When I arrived the most amazing thing was the amount of blood everywhere. It was plastered across the front of the building," he said. "Then I looked on the ground and you could see where the blood was coming from. There was also a lot of smashed glass and twisted metal everywhere."
BMA House was evacuated and the front of the building cordoned off as forensic teams moved in to search for evidence.
University College Hospital near Euston declared a major incident at 9.30am and the first casualty was admitted 15 minutes later. A group of student doctors described how patients were wandering bewildered through the corridors, many in floods of tears, shaking, in deep shock and covered with blood.
Professor Jim Ryan, a senior A&E consultant who led the major incident team, said: "One of the things that has characterised this episode is the number of senior staff on site within moments. It has been really wonderful to see. Even the builders working on a site have been offering to donate blood."
At St Bartholomew's Hospital in Smithfield, two police officers on motorbikes with sirens wailing and lights flashing escorted a blue Transit van to pick up supplies. As the officers waited patiently in the drizzle by the stone archway, medical staff swiftly filled the vehicle before it headed to other hospitals in the capital.
Referring to the evident shortage of ambulances and the stream of escorted civilian vehicles, one officer said: "We're using anything and everything we can get our hands on at the moment. We don't have much choice in a situation like this."
While its sister hospital, the Royal London, was the destination for most of the casualties from the attacks in the City, staff at St Bart's were working frantically behind the scenes. The atmosphere was one of subdued shock inside the hospital's minor injuries department, where staff remained on standby to treat the walking wounded.
While sirens wailed in the eerily empty streets outside, the sound of television news reports filled the corridors.
The hospital maintained its pivotal role in supplying both medicine and staff to those in need. There were also plans to transfer non-bomb related casualties at the Royal London to St Bart's in order to free up beds.
One ambulance worker said: "It's pretty difficult getting around and delivering supplies between hospitals but we're certainly doing the best we can."
Injured passengers among the 208 victims taken to the Royal London praised the medical care they had received. Thirteen had surgery and 39 were detained, three in the intensive care unit.
Paul White, the chief executive of St Bartholomew's and The Royal London NHS Trust, said: "This is probably the biggest incident we have had recently."
Alastair Wilson, clinical director at the Royal London, said that the hospital had received eight patients who were critically injured, including one who had suffered a heart attack.
The Royal Free hospital in Hampstead, north London, said that it had received 57 casualties. "We are seeing fractures, smoke inhalation, open wounds and burns," said a spokesman.
Nine people were admitted including three who underwent operations for fractures. None of the injuries was thought to be life threatening. The injured included two children - a four-year-old boy and one aged around 10. The older child was treated for smoke inhalation and the younger one had a check-up before being sent home. Guy's and St Thomas' NHS Foundation Trust said it had admitted 20 patients, three of them critically injured.
Six sustained major injuries and 11 minor. The problems ranged from smoke inhalation and burns to serious limb and chest injuries. Security staff patrolled outside St Thomas' Hospital, opposite the Houses of Parliament, where all routine appointments were cancelled.
Dave Morris, a Red Cross volunteer based at Liverpool Street from 9am, said: "In my 40 years with the Red Cross I have been involved with the Moorgate tube crash in the 1970s and a major fire in Dagenham, but this is an altogether bigger emergency."
Ron Mountain, a senior lecturer in disaster and emergency management at Coventry University, said that London's emergency preparations appeared to be working well.
The capital has been the scene of mock terrorist attacks in recent years in an effort to prepare the city's emergency services for such an event. Mr Mountain said that the blasts showed why such simulations were necessary.
"There has been a lot of work going on in the last couple of years, but you can never predict exactly what is going to happen or when it is going to happen.
"The main thing at the moment is the recovery of casualties. They need to be taken to hospital and the areas cordoned off to make sure there are no further unnecessary injuries."
Mr Mountain said that other cities would be watching and learning from what had happened in London over the course of the day. "Whenever these major incidents occur, everybody will be looking to see what lessons can be learned," he added.
The main hospitals
A total of 49 victims were brought here. Doctors had to amputate the limbs of some of them. Hundreds of medical staff were mobilised. Six consultant general surgeons and four consultant plastic surgeons led treatment teams. Staff said the atmosphere had been very calm. One medical student said: "There were a lot of cuts and some amputations. There was some initial panic, but everything soon calmed down.'' An emergency room was also set up at nearby Birkbeck College.
The streets of Whitechapel were brought to a standstill as 208 casualties arrived.Severely injured patients were wheeled into hospital, their faces blackened with soot and blood. Helicopters and ambulances brought wounded, and about 170 walking wounded were brought on six buses.
Victims started arriving at this Paddington hospital at about 10am. There were 38 casualties, seven of them critically injured, including some who had lost limbs and a further 17 with serious injuries, including smoke inhalation, burns, cuts and broken bones. Julian Nettel, the chief executive, said: "We have tried and tested procedures. Staff have pre-arranged instructions ... that worked very well this morning.''
GREAT ORMOND STREET
The hospital treated 22 casualties, 18 of whom were detained overnight. Two had surgery and one was in intensive care. Two of the wounded were the hospital's own medical staff, who had been on their way to work. Jane Collins, the chief executive, said: "Within half an hour our staff restaurant was completely cleared and equipped for triage." Today's out-patient services have been cancelled.Reuse content