The Texas Department of Transportation planned to keep the southbound lane of Interstate 35 just south of Loop 1604 closed until at least midnight as crews worked to clear the scene where an 18-wheeler burst into flames.
Bexar County Sheriff's officials said the 18-wheeler just burst into flames as it was traveling South on I-35 around noon.
Sheriff officials said they don't believe anyone was hurt.
However, traffic was backed up about a mile most of the day.
As of 4:30 p.m. on Wednesday, the southbound lane of the highway was still shut down as crews waited for another Hazmat crew to arrive.
Officials with the Bexar County's Fire Marshal's office said they were trying to determine an unknown substance that the truck was carrying at the time of the accident.
They said the papers burned up and that the truck was not properly tagged.
Fire marshals said when the first Hazmat crew arrived, they didn't have sufficient materials to clean up the mess.
So they had to call for another hazmat crew.
The accident is still under investigation.