AUSTIN, Texas (AP):

Investigators pursuing a suspected serial bomber in the Texas capital shifted their attention yesterday to a FedEx shipping centre near San Antonio where a package exploded on a conveyor belt in the middle of the night and caused minor injuries to a worker.

Although the latest blast did not inflict serious harm, it added to the widening fear of more strikes like those that have already killed two people and badly wounded four others.

Hours after the explosion, police sent a bomb squad to a FedEx facility outside Austin's main airport to check on a suspicious package that was reported shortly before sunrise. There was no immediate word about whether that package contained explosives.

Investigators also closed off an Austin-area FedEx store where they believe the bomb was sent to the distribution centre. Authorities roped off a large area around the shopping centre in the enclave of Sunset Valley.

FBI agent Michelle Lee said the explosion happened around 1 a.m. at a FedEx facility in Schertz, which is just northeast of San Antonio and about 60 miles (95 kilometres) southwest of Austin.

"It would be silly for us not to admit that we suspect it's related" to the other four Austin bombings since March 2, Lee said. She did not have details about the size, weight or description of the package.

One worker reported ringing in her ears. She was treated at the scene.

Before it exploded, the package had been sent from Austin and was addressed to a home in Austin, Texas Attorney General Ken Paxton said.

Police initially reported finding an unexploded parcel at the same FedEx facility, but later said they were mistaken and that the only bomb found was the one that exploded.