Texas Governor Rick Perry is calling Wednesday's deadly fertilizer plant explosion "a truly nightmare scenario."
Rescue workers are searching still smoldering ruins for survivors of the explosion that leveled homes and businesses in the town of West.
Police said it is not clear how many people remain trapped in the rubble, but said as many as 15 people may be dead, more than 160 injured. Several are missing.
Police said responders are still in the "search and rescue'' phase, as they go house to house. About 80 houses within a five-block radius were either heavily damaged or destroyed.
During a news conference, Governor Perry said much of the information about victims remains "very preliminary." He said U.S. President Barack Obama has offered to quickly declare West an emergency disaster area eligible for federal aid.
West's 2,800 residents were evacuated. Authorities have not determined the cause of the disaster.
An official with the Texas Department of Public Safety described the scene.
He said, "I can tell you I was there. I walked through the blast area, I searched some houses earlier tonight. Massive, just like Iraq, just like the Murray building in Oklahoma City. Same kind of anhydrous [chemical compound] exploded, so you can imagine what kind of damage we are looking at there."
Authorities have not determined how the initial fire started at the plant. Patrick Swanton, spokesman for the Waco police department, said the site is being treated as a crime scene, but insists there is no evidence to suggest it was anything other than an accident.
A nearby high school football field was turned into an emergency staging area to treat the victims.
Emergency crews from dozens of nearby towns and counties traveled to West to assist with the response. Texas Governor Rick Perry said state resources have been mobilized to provide assistance to local authorities.
Some information for this report was provided by AP and Reuters.