Hart, 40, was riding in a 1970 Plymouth Barracuda in Calabasas when driver Jared Black lost control of the vehicle and it rolled down an embankment, trapping two of the occupants inside of the vehicle, according to the California Highway Patrol.
Authorities said Hart and Black suffered "major back injuries," but didn't offer specifics. A third passenger, Rebecca Broxterman, did not suffer any substantial injuries, police said.
Hart's frequent movie co-star, Dwayne Johnson, was one of many sending well wishes to the comedian.
"Stop messing with my emotions brother @kevinhart4real,'' he wrote on Instagram. "We have a lot more laughing to do together. Love you man. Stay strong."
Bryan Cranston, who co-starred with Hart in "The Upside," asked everyone to "send him positive energy and healing thoughts."
"He’s a good human,'' Cranston wrote. "Get well soon, brother."
Nicole Kidman, who also starred with Hart in "The Upside," wrote: "Sending love and prayers to you Kevin."
Terry Crews, who was in the comedy "Soul Plane" with Hart, wrote for him to "get well soon brother."
Fellow comedian and roast master Jeff Ross wrote that "we need @KevinHart4real to be okay."
Several other comedians also sent out their support for Hart.
Hart was eventually transported and treated at Northridge Hospital and Medical Center. The driver was not determined to be under the influence of alcohol at the time of the crash, police said.