At least five people died on Sunday in South Texas after an S.U.V. carrying a dozen unauthorized immigrants crashed while trying to speed away from Border Patrol agents and local officials, the authorities said.

Several others were injured when they were ejected from the S.U.V., which was speeding about 100 miles per hour when it rolled over, the authorities said. The crash happened in Dimmit County, about 125 miles southwest of San Antonio.

Marion Boyd, the Dimmit County sheriff, said two United States citizens — the driver and one passenger — were trying to smuggle 12 unauthorized immigrants. He said his office would work with federal officials to charge the driver and the passenger, adult males who had not been identified.

The crash is also being investigated by the Texas Department of Public Safety, the United States Border Patrol and other federal agencies.