Frightening Convoy of Flashing lights

Last night (Dec 28) while driving east on the Belt Parkway, I was suddenly surrounded by a convoy of approx 50 unmarked mini vans.  All with their hazard lights flashing.  All driving erratically and disobeying traffic laws.  This went on for approx 5 - 6 miles.  I had my young daughter with me and both of us were frightened by the ordeal.  They caused me to break, speed up, slow down and change lanes as they were driving as if they owned the road often cutting in front of me.  I was wondering if anyone knows what this could be all about.  I doubt very much they were unmarked police cars.  Then again, I also wonder how so many of them could drive so crazy and not a cop in sight.