A woman was knocked down as she crossed the road in Morden.
The accident happened near the Harvester restaurant on the A24 London Road northbound.
The woman, believed to be in her 20s, was hit by a Vauxhall van around 2.50pm.
She was taken to St George's Hospital in Tooting with serious head injuries.
Police said she has 'life-changing injuries'.
The road is closed by Morden Park and traffic is queuing at the A239 Central Road.
A passer-by said: "There were lots of police cars and the person who was hit was hidden behind towels by ambulance staff.
"I saw a furry boot lying in the road and a rucksack, but they were a good five metres apart.
"There was what looked like a defibrillator too. It looked really serious. I hope they are alright."
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