Thursday update: Avicii, whose real name is Tim Bergling, posted on Twitter after hearing about the medical issues during his TD Garden show.
"Just hearing the awful news abt tonight. Its a terrible thing, I rly hope everyone is ok! My thoughts go to those affected & their families," Avicii posted on Twitter at about 1 a.m.
Multiple people were taken to local hospitals and a mass casualty incident was declared after several people needed treatment at the TD Garden Wednesday night during an Avicii concert.
Multiple city and private ambulances were called to the TD Garden Wednesday night. A Boston EMS spokeswoman said at about 10:30 p.m. that city ambulances transported at least three people to a hospital and that there was the potential for more patients to be transported. More than three dozen people were taken to hospitals after taking a dangerous substance, an EMS worker told the Globe.
The spokeswoman would not comment on the nature of the injuries or how many people were transported by private ambulances.
A spokeswoman for the TD Garden said there were "a number of transports due to medical issues."
A dispatcher at Cataldo Ambulance Service and a Boston police spokesman would not comment.
A level 2 mass casualty incident was declared at the Garden. Mass casualty incidents are generally declared to alert area hospitals to expect a certain number of incoming patients.
Popular Swedish DJ Avicii was performing at the arena Wednesday night. The dance and electronic music artist is on his True Tour.
A similar scenario played out last month in Toronto when Avicii played at the Rogers Centre and 29 people were taken from the arena to hospitals for illnesses related to alcohol or drugs, according to the Toronto Star.
Follow Michael Naughton on Twitter @metrobosmike.