SAN DIEGO -- A pipe bomb blast shattered the glass in the front door of a Federal Express distribution facility in the Webster area Friday and a second pipe bomb was discovered in the parking lot and was safely defused, police said.

The blast occurred in the 1600 block of 47th Street and Federal Boulevard at 1:47 a.m., according to San Diego police Sgt. Kerry Tom.

An employee inside the building initially thought some boxes had fallen over, said Tom, adding that the employee was not hurt.

When firefighters arrived, they found a second pipe bomb in the parking lot and safely defused it, the sergeant said.

"Two pipe bombs were left in front of the door. One detonated causing damage, the other was thrown into the parking lot and we rendered that one safe. We are assuming by what we saw that they were together, and the explosion of the first one pushed the second one into the parking lot," Metro Arson Strike Team Capt. Paul O'Brien said. "We have a lot of evidence we are going to have to process and we have to interview the people who work here."

The Metro Arson Strike Team was called to the scene to investigate the bombing, Tom said. There were no immediate arrests.