the location is reported to be near the Parchin nuclear facility. An alternative location is appears to be possibly at/near Khojir, known to be where a missile production and testing facility is located and is close to Parchin.
social media reports of emergency personnel and equipment headed to the site.
.Iranian state TV are confirming a blast but not where it is/was. there is a great deal of confusion with no official word yet.
Video from thedonald.win of the explosion. Not a gag, looks like a security camera caught it from a distance.