A woman was struck by a car before the driver picked her up and put her inside, according to eyewitness reports.
The incident, reported by the Sutton and Croydon Guardian, closed Beddington Lane in Sutton while detectives investigate.
Witnesses quoted by the paper say a man and a woman were arguing near a BP garage before the man drove a car into her, picked her up and put her in the vehicle before driving away.
The Met Police confirmed on Tuesday a woman is in a “potentially life-changing condition” in hospital, but did not confirm she was hit by a car.
Police were told that a man and a woman were seen having an “altercation” before she was forced into the vehicle on Monday night.
A spokesperson for the Met said: “Police were called at 9pm on Monday, 17 February to reports of a concern for safety of a woman on Beddington Lane, Sutton.
“It was reported that a man and a woman were seen having an altercation before the woman was forced into the car.
“Officers were later notified by the London Ambulance Service that a woman, believed to be the same individual, had been taken to hospital from a nearby address.
“She currently remains in hospital in a potentially life changing condition.
“It is believed the individuals were known to each other.
“Enquiries continue; no arrests have been made.”
Eyewitnesses said he saw a couple arguing when the woman sat on the man’s bonnet and refused to get off.
The driver then reportedly set off and ran over her before putting the woman in the car and driving off.
The victim’s condition when she was put in the car is unknown.
BP worker Hemat, 56, said the girl had been trying to get her phone back from the man and sat on the car bonnet.
“He then drove off at at least 30 mph with her still on the car bonnet. Then she must have slid off the bonnet as he turned right onto the road.”
Dave Wightwick, the owner of the Harvest Home pub down the road, said: “A local resident saw the car driving very, very slowly and the woman walking alongside it, arguing with the male driver.
"He shouted ‘Get into the car!’ and she was screaming and shouting.
“All of a sudden he deliberately swerved off the straight and narrow and hit the woman hard enough to knock her clean off her feet. She landed on her head with a whack.”
Two people ran over to help and the man pushed one away, he said.
Mr Wightwick added: “He then launched the injured woman into the car’s front foot-well.
“One of the witnesses was crying and screaming hysterically. He shouted saying he was going to take the woman to hospital and then sped off. He wasn’t hanging around.”
He said the man and woman had argued as if they were a couple.
Mr Wightwick added: “It’s terrible, absolutely shocking.
“The guy is an absolute lunatic. He wasn’t listening to reason. I hope the girl makes a full recovery.”