Paul Walker -- best known for his role in "The Fast and the Furious" movies -- died Saturday afternoon after a single-car accident and explosion in Southern California ... TMZ has learned.
The accident happened in Santa Clarita -- north of Los Angeles -- and according to multiple sources connected to Paul ... the actor was in a Porsche when the driver somehow lost control and slammed into a post or a tree ... and then the car burst into flames.
We're told Paul and another person in the car were killed. Law enforcement is still on the scene, and we're told the L.A. County Coroner's Office is on the way.
At this point, it's unclear what caused the accident, or who was behind the wheel when it happened.
Paul was 40 years old.
Sources close to Paul tell us he was in Santa Clarita for a car show to support the Philippines typhoon relief effort, and had been taking friends out for rides in his new Porsche GT. The accident happened during one of those test spins.
A rep for the actor confirms Paul died today in the crash after leaving a charity event.