Austin/San Antonio, Texas: A homemade bomb blew up at a FedEx Corp distribution centre near San Antonio early on Tuesday, officials said, and the FBI was investigating whether it was linked to a series of four homemade bombs that struck capital city Austin this month.

Officials did not say if they believed the device, which exploded at the FedEx facility in Schertz, Texas, was the work of a "serial bomber" who police feared may be responsible for the four earlier devices, which killed two people and injured six others. One person received a minor injury, officials said.

The first three were parcel bombs left on residential doorsteps, while the fourth on Sunday was apparently set off by a trip wire. Police warned that the latest bomb had a more sophisticated design than the others.

The package exploded shortly after midnight local time at the facility, about 105 kilometres south of Austin, the San Antonio Fire Department said on Twitter.

Agents from the Federal Bureau of Investigation and the Bureau of Alcohol, Tobacco, Firearms and Explosives were on the scene and investigating, fire officials said. They did not give the address for the package, which was filled with nails and metal shrapnel.