A pit bull’s vicious attack has left a San Francisco woman with life-threatening injuries … and video of the aftermath shows the dog drenched in her blood.

The attack went down in the city’s Tenderloin neighborhood Tuesday morning before authorities found the victim with the dog standing over her … its face beet red with gore.

The video — obtained by CBS News — is pretty graphic and shows a police officer struggling to restrain the animal with a snare pole.

The victim was later treated by medics who rushed to the scene … before being taken to a nearby hospital. Her current condition is unknown.

As for the dog … cops say that while it was being restrained, it became unresponsive … before being declared dead at the scene.

The witness who called 911 — Ashley Powell — told CBS News … “She was walking by. The dog was with the owner. And the dog just jumped and attacked her. Just started pulling her, biting her hands, fingers, chest, face.”

The attack lasted for another 10-15 minutes, Ashley said … as regular citizens tried to pull the dog off the helpless victim.

She added … “I had residents up there saying, ‘Get the dog off of her, get the dog off of her.’ A lot of people were going up and trying to pepper spray the dog, but it was just still trying to attack the lady.”