Five people in cars were probably blown off a motorway in Garland, near Dallas. Another three bodies were found in nearby towns.
Reports say churches were destroyed, cars mangled and trees toppled across a wide area.
Weather officials are predicting that Texas and Oklahoma could suffer a “historic blizzard”, bringing up to 16in (41cm) of snow.
The storms across Southern US have been unusually powerful for winter.
Garland Police believed that “winds from a tornado that passed through” the town late on Saturday were the cause of car accidents.