at about 1:00 pm or so, as I was sitting in the AMTRAK/NJ Transit waiting area, an AMTRAK employee started telling people in the ACELA waiting area to leave. He then started telling us on the other side of the little barrier, that we had to leave as well.
As we left the area, yellow Police Tape reading "DO NOT CROSS" had been strung up around the center of AMTRAK's station cutting off the entry ways to the tracks below. While people on the North end of the 8th Avenue side left, those of us on the South side of things, just stood and watched.
Minutes passed as the the TSA and NYPD patrolled telling two people stupid enough to cross the tape to stand back. then, came a soft "boom" from under where I was standing. A few moments later, we were told to go to the 7th Ave side of the station if we were going to be boarding.
While on waiting for my train, another soft "boom" from below. Then, the "All Clear" announcement, and the NY Penn went back to normal