Massive fertilizer plant explosion in West, TX

A fertilizer plant in West, Texas caught fire and exploded last night. According to one eyewitness, "Every house within about four blocks is blown apart." The small town is north of Waco, and the early details are horrifying, including the collapse of a crowded nursing home. People reported hearing the explosion 45 miles away. The tweets have more detail, as does this MeFi thread. A sense of the size of the explosion can be garnered from this video.