Mr. Swanton said authorities didn't yet know if the fire and the subsequent explosion was an accident or intentionally set, according to the Associated Press.

WSJ: Fertilizer-Plant Blast Kills Five to 15 in Texas

The subsequent explosion produced a tremor similar to a small earthquake.

BBC: Texas Waco fertiliser plant blast search for survivors

To be sure, at the plant site the radiation has spiked to deadly levels after the fire at one reactor and subsequent explosion at a different reactor.

FORBES: Tracking Radioactive Drift from Fukushima Nuclear Plant