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The A226 West Hill in Dartford was closed this morning after a man was found unconscious.
The road was shut between West Hill Drive and Priory Hill.
The man is in a criticial but stable condition after being rushed to Darent Valley Hospital.
A police spokesman said they were called to the incident after the man collapsed.
Detective Inspector Ivan Beasley said the 33-year-old had collapsed outside a warehouse.
An ambulance spokesman said the man suffered a heart attack and was resuscitated at the scene.
He added the injuries were life threatening.
People living nearby said this morning that the first they heard about the incident was when police arrived.
Louis Jones, 23, of Church Court, West Hill Drive, said: "I heard loads of sirens.
"I looked out of my window and lights were flashing and there were lots of police cars, about five, and an ambulance."
Andrew Harding, 48, who lives on West Hill Drive, said: "Most nights there's something going on with people shouting, making lots of noise and throwing rubbish outside our flat.
"I find it quite scary because you never know what they are going to do."
The roads were re-opened at 10.45am. Police are reviewing CCTV footage of the area to establish what happened.