I was in the forecourt with Negasonic, Jubilee and Pixie. There was a single explosion on the ground floor which likely set off two larger ones. The propellant they used was probably a fairly stable one sourced from people who knew what they were doing. It didn't smell like any of the commonly found flammable liquids that would indicate amateurs. Immediately after the explosions as people began to react, several people pulled out guns and began to fire on the crowd. Mostly rifles, semi-automatic, though I noticed a few handguns and sawn off shotguns. There was a lot of yelling about mutants and I could smell smoke starting to fill some of the closed stairwells to keep people inside. The open escalator was turned off but many people made it down that way. I tried to remain on the outskirts of the bigger group to target anyone attempting to pick them off. The ground floor was mostly filled with smoke and there were several fires but we could navigate around them and once we got outside the emergency services and SHIELD were already arriving.