The chopper exploded in a ball of flames in a residential neighborhood Saturday afternoon. The person who shot the video lives across the street from where the helicopter crashed. He tells TMZ, he heard a loud noise coming from the helicopter and felt it was hovering too low.

The man saw the chopper "spinning around violently in the air" and suddenly a piece of the tail broke off and it flipped upside down and nosedived in the ground.

The chopper was monitoring the white nationalist rally taking place Saturday ... although it's unclear at this point what exactly caused it to go down. Two officers died in the crash.