Motorists are being asked to drive with caution on northbound U.S. 77 in Harlingen.
The accident happened on the northbound lanes of the highway just across from Valle Vista Mall just after 12 p.m. Monday.
Witnesses told Action 4 News that the back gate of the 18 wheeler suddenly opened causing all the asphalt to spill on the roadway.
Texas Department of Public Safety (DPS) state troopers are investigating the accident.
The highway remains open but drivers are asked to drive with caution through the area.
Authorities reduced the highway to one lane while a clean up crew removed the debris from the roadway.