Walker and his friend and financial adviser Roger Rodas died in the one-car crash Saturday in the Southern California community of Valencia.
The street where the crash happened forms a loop amid commercial buildings that is isolated from traffic, especially on weekends.
California Highway Patrol Sgt. Rick Miler calls the neighborhood "a hot spot for street racers."
The Los Angeles County Sheriff's Department is still investigating, but already has said speed was a factor.
Walker's publicist said the action star was Rodas' passenger.
Fans of Walker continued to gather Monday at the site about 30 miles northwest of Los Angeles, leaving flowers and memorabilia from the movie franchise about fast cars that made him famous.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
Fans of "Fast & Furious" star Paul Walker erected a makeshift memorial near the site of his fatal automobile crash, as investigators worked to determine the cause of the fiery weekend wreck that also claimed the life of his friend.
The Los Angeles County Sheriff's Department said speed was a factor in Saturday's one-car crash, though it will take time to determine how fast the car was going.
Roger Rodas, Walker's friend and financial adviser, also died, according to Walker's publicist, Ame Van Iden. She said Walker was a passenger in the 2005 red Porsche Carrera GT when they drove away from a fundraiser in the community of Valencia, about 30 miles northwest of downtown Los Angeles.
Sheriff's deputies found the car engulfed in flames when they arrived at the site of the crash, near the fundraiser at Rodas' sport car dealership. Officials have not identified either person found in the car.
Because Walker is so closely associated with the underground culture of street racing portrayed in the popular film franchise, the accident had an eerie quality - a tragic end for a Hollywood hero of speed.
On Sunday, fans of Walker, 40, gathered to leave flowers, candles and memorabilia from the action movies. His "Fast & Furious" co-star Tyrese Gibson broke down when he visited the crash site.
"Paul is the heartbeat of this franchise and we're gonna see to it that his energy and presence lives on forever," Gibson later posted on his Instagram account.
Sheriff's deputy Peter Gomez said investigators were trying to determine how fast the car was traveling and what caused it to go out of control, including whether the driver was distracted or something in the road prompted him to swerve.
After the Porsche crashed into a light pole and tree, it burst into flames. The downed light pole had a speed limit sign of 45 mph.
Walker rode the "Fast & Furious" franchise to fame, starring in all but one of the six action blockbusters, beginning with the first film in 2001. He had been on break from shooting the seventh installment; production began in September and while much of the film has been shot, it's incomplete.
Universal Pictures has not said what it plans to do with "Fast & Furious 7," which currently is slated for release in July.
Walker and Rodas had thrown a fundraiser benefiting victims of the recent typhoon in the Philippines. The event was held by Reach Out Worldwide, a charity Walker founded in 2010 to aid victims of natural disasters.
The fundraiser and toy drive took place at Rodas' custom car shop, Always Evolving, in an area of warehouses and office parks. Rodas, 38, and Walker co-owned an auto racing team. Rodas competed in 10 Pirelli World Challenge GTS races this year, the racing organization said in a statement.
Attendees rushed to the crash, which was nearby but out of sight, to try to put out the flames with fire extinguishers.
One attendee of the event, Jim Torp, said he heard the loud sound of a car's engine revving and then an explosion. Walker and Rodas planned a quick ride, Torp said.
"The last words Paul said to anybody were, 'Hey, I'll be back in five minutes. All right?' And that was it," according to Torp.
Torp said Rodas had a young son, whom he tried to stop from running to the accident scene, but could not catch him in time.
Walker left behind two completed films. He stars in the upcoming Hurricane Katrina drama "Hours," which Lionsgate's Pantelion Films is to release Dec. 13. He also stars in "Brick Mansions," a remake of the French action film "District B13" that Relativity plans to release next year.
He is survived by his 15-year-old daughter.
Take ABC13 with you!
Download our free apps for iPhone, iPad and Android devices