Vin Diesel finally broke his silence on the death of his friend Paul Walker last night -- arriving at the crash site and thanking mourners for "showing that angel in heaven how much you appreciate him."

Diesel and Walker had appeared in several "Fast and the Furious" movies together -- and considered each other close friends off camera.

When Vin arrived to the crash site, a police officer allowed the actor to use the loudspeaker from a squad car to address the huge crowd ... and he delivered a heartfelt speech.

"To show the love that you have shown Paul ... it's gonna stay with me forever."