Walker was in Santa Clarita, CA when his Porche GT spun out of control and crashed into a tree. TMZ is reporting the vehicle caught fire and burst into flames. They also included that Walker was in the vehicle with an unidentified passenger and it is unclear on which person was driving at the time. Walker's rep confirmed he had been at a car show and was taking individuals on test drives of the vehicle to raise money and awareness for the recent typhoon that hit the Philippines. Walker was leaving said charity event at the time of the crash.
This is a surprise and rather sad. It's always unfortunate to see someone pass at a young age like 40. In case you never saw a Fast and Furious movie, Walker had also starred in Pleasantville, She's All That, Varsity Blues, and The Skulls. Walker was currently filming Fast and Furious 7 where he was reprising his role as Brian O'Conner, so I would expect some sort of delay on that one due to this. Universal has not yet commented regarding the status of Fast and Furious 7 or the tragedy.
[Update] Universal released the following 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."
It was also released via Walker's official Facebook that he was a passenger in the vehicle and was attending an event for his charity, Reach Out Worldwide, when the vehicle lost control and struck a light post. Police included that high speed was a factor in the crash.