The people reported two explosions in fast order. This would be typical of a grain explosion(s). The first grain explosion kicks up additional grain dust which then ignites in a second explosion which is usually larger and more deadly than the first, we'll see.
This incident reminds me of Texas City in 1947. I also remember an incident at the height of the space race with a fire and massive explosion at a site where fuel was made. You saw the sound wave 3-4 seconds before you heard the explosion. Prayers for the members of the Fire Brigade, you just know it has to be deadly for them.