At least six people died and eight were injured when a pickup truck smashed into an 18-wheeler on a South Texas highway early Thursday, state transportation officials said.

The accident happened about two miles north of Falfurrias when the driver of a Ford F-150 missed a traffic sign and drove onto U.S. 281, hitting the 18-wheeler that was hauling cars, Department of Public Safety spokeswoman Lisa Block said.

Investigators were still at the scene at about noon, six hours after the wreck, and the victims weren't identified. Block said it was possible more bodies would be found.

Five men and one woman were killed, Customs and Border Protection spokesman Roy Cervantes said. Cervantes said some people in the truck were suspected illegal immigrants. Witnesses said people jumped from the vehicle and ran into the brush.

U.S. Immigration and Customs Enforcement is investigating.

Block said officials don't know where the deceased are from but that most of the injured are from Mexico.

Two of the injured were flown to Corpus Christi Memorial Hospital; the remaining were taken to Alice Spohn Hospital in Alice.

U.S. 281 between Falfurrias and Premont was to be closed into the early afternoon.

Falfurrias is about 170 miles south of San Antonio.