Walker, 40, was a passenger in the red 2005 Porsche Carrera GT that crashed into a utility pole and burst into flames in the city of Santa Clarita on Saturday afternoon (local time).
"Speed was a factor in the solo vehicle collision," the Los Angeles County Sheriff's Department said in a statement.
Deputy Mark Pope said the accident was under investigation and he did not know how fast the car was going.
The Los Angeles Times identified the driver as Roger Rodas, 38, a friend of Walker's who owned Always Evolving, an auto dealership and racing services company.
The sheriff's department would not confirm that. The company could not be reached for comment on Sunday.
In a message on its Facebook page, the company posted a message that said, "Thank you all for your condolences and prayers while we mourn the loss of our loved ones."
The blond-haired, blue-eyed Walker was in five of the six "The Fast and the Furious" films about illegal street racing and heists. A seventh installment was in development, according to Universal, the studio behind the franchise.
Walker played law enforcement official Brian O'Conner in the movie series.
