Residents spoke of their shock today after a crash between a lorry and a bus in the morning rush hour.
Firefighters had to cut passengers free after the double-decker bus toppled on to its side.
The driver of the C3 bus was one of five people seriously hurt, along with four passengers, after the incident in Plough Road, Clapham, south-west London.
One report said the lorry was carrying railway track girders which apparently smashed the bus's windows.
A local 45-year-old mother-of-two, who declined to give her name, said: "I heard the ambulances going by and went down the road to see what had happened.
"I saw a lady on a stretcher being put into an ambulance and I was crying because I don't like to see things like that. I've never seen anything like this before."
Another Plough Road resident, John Lipnicki, 53, an architectural technician, said: "There are some places round here where you have to be very careful crossing the road, but I've not known anything happen down there.
"I asked an officer if anybody had been hurt, and he said there had been injuries."
The bus was taken away a few hours after the crash. Some of its upper windows were smashed and it seemed to be gouged on the side.
The lorry was still there at that time and some streets remained cordoned off.
Police said the male driver of the lorry was arrested and is in custody at a south London police station.
Three of the passengers were cut free by firefighters from Battersea in Wandsworth.
Police said that as well as the four passengers and the driver who were seriously hurt, a further 13 needed hospital treatment for their injuries.
London Ambulance Service said a 27-year-old woman and a 30-year-old man were taken "as a priority" to St George's Hospital, Tooting, south London, while another priority case, a 30-year-old man, was taken to Chelsea and Westminster Hospital.
Other injured people were taken to Chelsea and Westminster, St Thomas' and Charing Cross Hospital.
The C3, run by the Abellio Company, operates between Earl's Court and Clapham Junction.
Transport for London said there would be a full investigation into the incident.