"All of a sudden I could see the walls move both ways," Moore said in a telephone interview. As he and his friend drove closer to the explosion on Interstate 35, the smell became so strong their eyes started burning, he said.
The U.S. Chemical Safety Board, which investigates industrial chemical accidents, said on its website it deployed a "large investigation team" expected to arrive Thursday.
The blast came two days before the 20th anniversary of the U.S. government's raid on the Branch Davidian sect in Waco that killed 76, including cult leader David Koresh. In revenge for that incident, exactly two years later Timothy McVeigh detonated a truck bomb containing ammonium nitrate in front of the Alfred P. Murrah Federal Building in Oklahoma City, killing 168 people.
Mildenberg reported from Austin, Texas, Marois from Sacramento, Calif. Contributors: David Wethe in Houston, Thomas Biesheuvel in London and David Stringer in Melbourne.