Walker was apparently the passenger in a red Porsche that crashed Saturday afternoon, soon after the actor attended a charity event.
Sheriff's officials said speed may have been a factor in the crash, which took place on a normally quiet street with a 45 mph speed limit. The Porsche was badly burned and mangled.
Witnesses said the car was fully engulfed in fire.
"When I went out there, it was just smoke. Just black smoke. I thought it was a brush fire," Alyssa Yorton told the Los Angeles Daily News.
"It was engulfed in flames. There was nothing. They were trapped," Antonio Holmes, who said he was a friend of Walker's, told the Santa Clarita Valley Signal. He added the actor had been at a charity event earlier in the day. Holmes said the Porsche appeared to hit a tree and then slam into a light standard.
KTLA News reported that debris from the crash shattered a window in a nearby building.
The single-vehicle crash occurred about 3:30 p.m. in the 28300 block of Rye Canyon Loop.
The cause of the crash is under investigation, sheriff's Deputy Kim Manatt told The Times.
According to a statement posted on his
"It is with a truly heavy heart that we must confirm that Paul Walker passed away today in a tragic car accident while attending a charity event for his organization Reach Out Worldwide," the statement said. "He was a passenger in a friend's car, in which both lost their lives. We appreciate your patience as we too are stunned and saddened beyond belief by this news."
Universal Pictures released a statement:
"All of us at Universal are heartbroken. 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. We send our deepest and most sincere condolences to Paul's family."
At the time of his death, Walker, who also starred in "Pleasantville" and "Varsity Blues," was working on the seventh film of the "Fast and Furious" franchise.
There was a growing memorial at the crash site as people paid their respects.