Roger Rodas, a friend of Walker, also died in the fiery crash, which occurred near Rye Canyon Loop and Kelly Johnson Parkway.
Deputies from the Los Angeles County Sheriff's Department's Santa Clarita Valley Station responded to that location around 3:30 p.m. and found a red Porsche Carrera GT that had crashed into a tree and light pole and was engulfed in flames. People in nearby buildings grabbed fire extinguishers and ran to try to help put out the blaze.
"We heard the crash; we heard the explosion, and we got up here as quick as we could to find out what it was," said Jim Torp, Walker's friend.
"There was nothing...we tried...went through fire extinguishers and...," said Antonio Holmes, a friend.
L.A. County firefighters arrived, extinguished the fire and found the two victims inside the vehicle, sheriff's officials said. Both were pronounced dead at the scene.
Investigators said that speed was a factor in the crash.
The 40-year-old actor had attended a charity event at a nearby business he owned called Always Evolving Performance. Toys were being collected for Walker's foundation named Reach Out Worldwide.
Friends said Walker, a car enthusiast, decided to go for a ride with Rodas, a businessman and professional race car driver. Rodas was believed to be driving the car.
"When we saw Paul and Roger leave, Paul was the passenger in the vehicle," said Torp.
"Him and his buddy, his brother in heart Roger, they decided to joyride, take a spin, something that we all do," said Holmes.
Ed Winter of the L.A. County coroner's office said because of the fiery crash, he can't positively identify the bodies.
"It's going to take some time. We're going to have to probably use dental and possible medical X-rays," said Winter.
An autopsy is scheduled for the next couple of days. The exact cause of the crash remains under investigation.
Movie fans and fellow actors were stunned when they heard the news of Walker's death. Fans of the "Fast and Furious" franchise began seeing posts on social media that they at first did not believe.
"Facebook, like tweets everywhere. I was on my phone for one minute and all the statuses just blew up, and just he's gone," said Shahrir Islam, a fan.
"All of the parts, the roles that he had, he adapted really well and like very believable actor and character," said Natalie Josefsberg, a fan.
Walker starred in all but one of the six "Fast and Furious" movies and was working on "Fast and Furious 7" at the time of his death. He also starred in the suspense drama, "Hours," a movie that is set for release this month.
"All of us at Universal are heartbroken," Universal Pictures said in a statement. "Paul was truly one of the most beloved and respected members of our studio family for 14 years, and this loss is devastating to us, to everyone involved with the 'Fast and Furious' films, and to countless fans."
Several celebrities, including his "Fast and Furious" co-stars, took to social media Saturday evening to share their thoughts.
Vin Diesel posted a photograph of him and Walker arm-in-arm on Instagram with the message: "Brother I will miss you very much. I am absolutely speechless."
"Your humble spirit was felt from the start," Ludacris said on Twitter. "Wherever you blessed your presence you always left a mark, we were like brothers."
Tyrese posted on Instagram: "My heart is hurting so bad no one can make me believe this is real Father God I pray that you send clarity over this, cause I just don't understand My heart hurts it's broken no one can convince me that this is real....Prayer warriors please pray real hard for his only child, his daughter and family."
Actor and comedian Kevin Hart tweeted, "I'm a devastated right now. My prayers & condolences go out to Paul Walkers family & friends. He was a amazing talent & will truly b missed."
Walker grew up in a working class, Mormon L.A. household. He was the son of a fashion model and a sewer contractor. The oldest of five siblings, Walker's mother began taking him to auditions as a toddler. He was a child model beginning at the age of 2.
Walker is survived by his 15-year-old daughter.
The Associated Press contributed to this report.