Initial tests showed the device contained ammonium nitrate, the same volatile substance that sparked a massive explosion last month at a fertilizer distribution plant 110 miles north in West, Texas, said Austin fire Lt.

CNN: Austin bomb an amateur job or something more insidious?

The situation remains volatile because of an extremely dangerous substance, ammonium nitrate, found at the scene, said an official from the county sheriff's office.

BBC: Texas Waco fertiliser plant blast search for survivors