The videos showed the smoke from the first blast and very numerous smaller explosions at the base of the fire, suggesting ammunition or fireworks were being detonated.
The the really big main explosion occurs, generating an ascending shock wave that condenses the water vapor in the air as it expands and demolishes the large apartment building near it.
It was incredible that anyone would store 2,700 tons of ammonium nitrate anywhere in close proximity to anyone, much less a major city - normal safety precautions would have required dividing that explosive into smaller amounts and storing it in bunkers away from any people. (When I was in the Defense Nuclear Agency, we used 5,000 tons of ammonium nitrate to simulate a low-level nuclear event - but that was far out in the desert).
The real mystery is what else was involved in the first detonation and the smaller detonations that preceded to main blast - and why that much explosive material was stored so close to a city.
I was at Minor Scale and Minor Uncle. We had a blast.