One wounded employee was taken to hospital after suffering a mild injury in the explosion at the distribution center in Schertz, northeast of the city.
The package detonated as it was moving from one conveyor belt to another and the staff member was not hit by the contents, local news reports.
Federal agents say the package is likely linked to four other attacks this month in Austin, some 80 miles north-east of San Antonio, that have left two dead and four injured.
Authorities say a ‘serial bomber’ is at large and have warned that the devices appear to be getting more sophisticated.
FOLLOW THE LINK FOR THE FULL REPORT – JR