Here's a handful of chemicals that are both water reactive and either emit flammable gasses or strong oxidizers:
Aluminum phosphide, ethyldichlorosilane, ferrosilicon, lithium amide, phosphorus heptasulfide, trichlorosilane
Bromine pentafluoride, bromine trifluoride, iodine pentafluoride, sodium peroxide
Then there's the discussion of the possibility of something like calcium carbide being present, which when wetted produces acetelene gas, one of the most easily ignited explosive gasses on earth.
However, at this point it's all just guesswork. If this were the US, we would have a accurate inventories of what was on sight and even if lost, we would have accurate records of deliveries. We may never know the exact chain of events in this case because the first responders are all dead, the point of ignition is so badly damaged and because accurate records likely never existed, no less off site. We should eventually get enough information about what was involved through trace analysis, but exactly how much, probably not. They might reverse engineer the damage to guess.
We have had any number of similar blasts in the US; the blast at the Texas fertilizer plant comes to mind, but for the most part we have zoning and other regulations that isolate this stuff in large quantities. Imagine Pepcon going up in the middle of the port of Long Beach... Despite the loss of life and property in china with this incident, it could have been a lot worse.
