She declined to give her name.
Police said the medium-sized box exploded on the conveyer belt.
A map showing details of the four previous bombings in Austin.
Authorities are investigating a suspicious package at a FedEx Facility in Austin.
The investigation into the Schertz blast was slowed by the need to ensure the FedEx facility was safe, FBI Assistant Special Agent in Charge James Smith said at a midmorning update. It hurt one person and federal agents said the package bomb was likely linked to the bombs in Austin. Police are still investigating the second most recent attack that occurred Sunday evening, injuring two young men. Police said another was probably activated by a tripwire, triggered by two men walking along a street in south-west Austin.
Police issued revised safety guidelines to Austinites today, urging them to "remain vigilant" and to stay away from suspicious packages they may see in their neighborhoods.
Texas police believe a serial bomber may be behind four explosions in state capital Austin this month that have left two people dead and four others injured.
In all, two people have been killed and four have been injured in the Austin explosions.
This time the explosion rocked a facility in the town of Schertz, in the San Antonio area.
The FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are responding to the scene, sources told ABC News.
A FedEx worker was injured after a package containing nails and shrapnel blew up at a distribution centre in Schertz, San Antonio Fire Department said.
"As each tip comes in, it gets assigned to either a team of Federal Bureau of Investigation agents, ATF agents or Austin Police detectives to do follow-up work on", he said.
When the package exploded, about 75 people were inside of the building.
One person was treated at the scene for a non-life-threatening percussion-type injury, officials said.
The suspect "could be engaging in these new behaviors in an attempt to challenge reports characterizing him as inexperienced and prove true those that reference his high level of sophistication". However, both of the victims of Sunday's attack were white and the apparent use of a tripwire "suggests a perpetrator aiming for random targets", says The Guardian.
The Austin police chief's direct appeal, complete with promises to listen to the bomber and try to understand the reasons, reflects the stubborn progress of the investigation in which there's no known motivation and the ties between the victims are opaque at best.
Three members of the Congressional Black Caucus called Monday for federal officials to classify the bombings as terrorist attacks and determine whether they are "ideologically or racially motivated".