Fire Capt. Doug Blackburn said the rig was about 60 miles north of Dallas, traveling north on U.S. Highway 75, when it crossed the median and crashed into a pickup truck and then into a sports utility vehicle.
Television video showed the pickup nearly sliced in half and the SUV overturned. "The vehicles are burned pretty bad," Blackburn said.
He said the SUV was so charred its license plate could not be read.
Five people - a mother, a grandmother and children ages 8, 3 and six weeks - died in the SUV, Blackburn said. The bodies of five adults were found in and around the pickup truck.
The injured - including the tractor-trailer driver - were taken to hospitals in Dallas and Sherman.
Authorities did not immediately know what caused the driver to cross the median.
By Liz Austin