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Kevin Hart's car careened off the road, a witness surveyed the damage and called 911 to report there were people stuck, and first responders would need to cut them out of the vehicle.

The male caller said there were 2 people stuck, but "There was 3 [people] I guess" -- referring to the fact Kevin's security had already taken him from the crash scene.

The caller said everyone was conscious, but "scared because they're stuck in there." He added, "The roof is crushed, the car is pretty totaled."

It sounds like there was at least one other civilian on the scene trying to help before cops and the fire department arrived. Something new we learned from this call is that the driver, Jared Black, was able to free himself from the car eventually.

The caller said Jared "looked hurt," but the woman -- Jared's fiancee, Rebecca Broxterman -- was still stuck inside the destroyed 1970 Plymouth Barracuda. You can hear him yelling to both Jared and Rebecca to "stay calm, help's coming!"

TMZ broke the story ... Kevin, Jared and Rebecca violently veered off the infamous Mulholland Highway around 12:45 AM Sunday morning. Both Kevin and Jared suffered what police called "major back injuries" ... while Rebecca was able to walk away with some minor pains.

We know Kevin underwent successful back surgery on Sunday night, but will need weeks of physical rehab before he's fully recovered. It's still unclear what Jared's condition is after being airlifted to UCLA Medical Center.

Police are investigating the crash and say excessive speed might have been a factor. As we reported, a witness reported hearing tires peeling out moments before hearing the car smash through a fence as it flew off the road.