On Thursday morning, firefighters search the debris in a neighborhood destroyed by a massive explosion at West Fertilizer Co in West, Texas. The explosion killed up to 15 people and injured more than 160, officials said overnight, however, the death toll is expected to rise. LM Otero / Associated Press

Grim anniversary

The explosion came two days before the 20th anniversary of a fire in nearby Waco that engulfed a compound inhabited by David Koresh and his followers in the Branch Davidian sect, ending a siege by federal agents.

Officials said flames that continued to smolder inside the fertilizer plant initially posed two threats: the possibility of setting off further explosions and the emission of hazardous fumes into the town.

Swanton said a residual fire burning underneath additional chemical tanks had been brought under control, "and I don't think that is any longer a threat".

Texas Public Safety Department spokesman D.L. Wilson said about half the town, about eight to 10 blocks, had been evacuated and that the other side of the town may have to be evacuated if winds shift.

But emergency management personnel determined that the smoke presented no immediate danger to the public, Swanton said.

Officials said a full assessment of property damage would not come until after dawn.