A double-decker bus crashed into a shop in south London leaving two women trapped on the top deck.
One eyewitness said he felt the bus drifting before it crashed into the front of the Poggenpohl Kitchen Design Centre in Lavender Hill, causing the shop front to collapse.
Another said the driver told her he had "blacked out", adding a paramedic thought he had had "some kind of fit".
The women were rescued by fire crews and the driver was taken to hospital.
London Ambulance Service said a total of 10 people had been treated by paramedics, three of whom had been taken to hospital.
It said it had sent five ambulance crews, two paramedics and an incident response officer to the scene at about 06:55 BST, along with an air ambulance.
Andrew Matthews, 34, from Wandsworth, was one of about a dozen passengers on the bus.
"I was on the top floor at the back, fortunately," he said.
"I noticed the bus drifting. I heard a smash and saw the roof of the shop going through [the bus] from the front left. It went to the fourth or fifth row.
"I wedged myself in, bracing myself. As soon as the bus came to a stop there was yelling, screaming.
"I noticed a lady wedged in the front right-hand side. She was screaming for help. There was a lot of blood."
Another passenger, nurse Amy Mullineux, 40, from Wandsworth, said the driver told her he had lost consciousness before the crash.
"I spoke to him. He said he blacked out before the bus hit the shop. He doesn't remember hitting anything.
"The paramedic told me they think he had some kind of fit."
A witness said smoke could be seen coming from underneath the bus.
Solange Morin, 33, who lives nearby, said: "I saw this woman shouting and banging on the glass. Everybody shouted 'fire, fire'.
"I went on to the bus. I talked to her and was holding her hands.
"She was pinned. I wouldn't have been able to get her out.
"She was so scared because people were shouting fire. There was a lot of smoke."
Another local resident, Brendan Pfahlert, said the crash "sounded like a large amount of glass being dropped".
A Transport for London (TfL) spokeswoman confirmed the crash involved a route 77 double-decker bus and said an investigation was under way.
Poggenpohl UK managing director Simon Richmond said: "We are relieved that no-one from our team was injured as the showroom had not yet opened for the day, but our thoughts are with the driver and passengers on the bus as we understand there have been casualties."
He said he hoped business would return to normal soon, but that the showroom had been severely damaged.
Police have appealed for any witnesses to contact them with information.
Detectives are particularly keen to hear from anyone with dash or helmet camera footage who was passing either prior to or during the crash.