I've just seen the video and some still photos from the news channels but it does look as if they lost part of the main rotorblade or all of it (video quality was poor and I'm a fixed wing, not helicopter ATP, so bear that in mind.) I don't know enough from the news to have any knowledge if it's a similar event but this made me recall an incident involving that same make and model (EMS helicopter in Indiana in late August of 2008, part of a blade failed, which then, if I remember correctly may have also struck the tail boom, but all aboard died on impact.)
www.ntsb.gov (public) has the report of that accident. Click on "Safety Research" on the dark blue top bar, then select "Accident Data" from the drop down, then click on "CAROL" (all caps light blue active link) then scroll down to "additional resources" and click on "monthly lists" and go to August 2008 and look fo
r NTSB # CHI08FA269 in Greensburg, IN. The Docket link has the AD and all the case information and photos. (I've attached a screenshot of the AD, which does include the serial number of the New York rotorcraft involved in this current accident.
From the August 2008 accident: "The National Transportation Safety Board determines the probable cause(s) of this accident to be: The in-flight separation of a main rotor blade due to a fatigue failure of the blade spar, rendering the helicopter uncontrollable, and the manufacturer's production of main rotorblades with latent manufacturing defects, which precipitated the fatigue failure of the bladespar."
I'm NOT SAYING THIS IS A FACTOR IN THIS ACCIDENT, since the AD was published in 2009 it would be highly unusual that it wasn't complied with and fairly easy for investigators to confirm with copies of the maintenance records.
FAA Initial Notification (public website)
https://www.asias.faa.gov/ (bottom of the page "accident and incident data" then go to "preliminary data" and look for the ASAIS link to view data for 4-11 (they always post the day AFTER the even, or on Mondays for the previous weekend).
FAA Aircraft Inquiry (public website)
https://registry.faa.gov/AircraftInquiry/Search/NNumberResult?nNumberTxt=216MH
N216MH Bell 206L--4 Serial Number 52296
My heart goes out to the families, the colleagues of the pilot, and the first responders.