PASSERS-BY looked on in horror as a woman was dragged under a lorry's wheels as she crossed the road in Hammersmith Broadway.
The collision, with an articulated Tesco lorry, happened at around 3.15pm on Wednesday.
The victim, believed to be in her early 40s, had been walking across a pedestrian crossing outside Hammersmith underground station.
Police, paramedics and firefighters went to her aid. She was found to be suffering multiple injuries and taken by air ambulance to the Royal London Hospital in Whitechapel, where she is in a serious condition.
The entire Hammersmith gyratory system was sealed off for around two hours while investigations were carried out.
The closure resulted in gridlock on roads already jammed because of the Tube strike.
Shocked witnesses described the situation unfolding as throngs of shoppers and office workers tried to cross at the busy junction next to the Edwards pub.
Nur Islam Pavel, handing out free newspapers at the scene, said: "I could see it happening. The lady fell to the ground and then the lorry carried on moving. We were shouting to the driver and eventually he stopped.
"When I went over there and crouched down she looked at me. I could see her leg wrapping around the wheel - It was horrible. I've never seen anything like it in my life."
Nasir Mehdi, who runs a newsagents stand in Beadon Road, said: "I just heard a scream, and then other women were screaming because someone was under the truck.
"I came out a few minutes later and the ambulance and police cars were already there and had covered her in a blanket.
"Two guys were underneath the truck and it looked like they were trying to get her out."
All roads leading into Hammersmith Broadway were sealed off by police tape, with massive tailbacks building up in Fulham Palace Road, Talgarth Road, Shepherds Bush Road and Hammersmith Road as commuters struggled to get home from work.
An ambulance service spokeswoman said two ambulances, two single responders, a cyclist responder and the air ambulance were all dispatched to the scene.