The explosion was reported just after midnight.
A package believed to be bound for Austin, Texas, exploded at a Texas FedEx facility overnight, law enforcement officials said early Tuesday.
There has been an explosion reported at a package facility in the San Antonio area.
This is the fifth bombing to have hit Texas since March 2, following a spate of explosions which have now left two dead and five injured.
None of the other 75 workers at the center were reportedly wounded by the parcel, which was said to contain nails.
"We are clearly dealing with what we expect to be a serial bomber at this point", Austin Police Chief Brian Manley told a news conference near the site of Sunday's bombing. All four devices were similar, police said on Monday.
The employee's injuries are not considered life threatening.
ATF and Federal Bureau of Investigation agents were on the scene, along with San Antonio Police Department SWAT and bomb squads.