Dozens of concertgoers were hospitalized during a show by superstar DJ Avicii in Boston on Wednesday night, CNN affiliates reported.
Local media put the number of patients anywhere between 30 and 80.
Massachusetts General Hospital told CNN it received 13 patients between ages 16 and 19. All of the patients are being evaluated, said Kory Zhao, a hospital public affairs officer.
Most patients had a problem with dehydration, drugs and alcohol, authorities told CNN affiliate WHDH.
Avicii, the Swedish artist behind the hit song "Wake Me Up," performed at the TD Garden as part of his True Tour.
Dozens of ambulances lined up outside the garden venue as crowds spilled into the streets after the concert. Other ambulances zoomed off, red lights flashing, as frazzled parents waited.
"I have a 15-year-old and her girlfriend that came to the Avicii concert ... we just heard about this, " Pam Jones told WHDH. "I'm very shocked. We have to find her."
Chanel Andre, who also attended the concert, said the venue was hot.
"These concerts should be outside ... I think it was a combination of heat and drugs, more of the latter," she said.
The artist, whose real name is Tim Bergling, became an international star as a DJ and producer in electronic dance.
His other hit songs include "Hey Brother" and "Levels," which was nominated for a Grammy for Best Dance Recording last year.
This is the latest incident involving concertgoers.
A man collapsed and died after leaving the Electric Daisy Carnival in Las Vegas on Saturday morning, the Las Vegas Sun reported. Avicii was on the schedule of performers at that festival.
It's unclear whether his death was linked to the festival. An investigation is under way.
Police told the newspaper that nearly 800 people were treated for medical conditions, 25 of whom were transported to local hospitals.
About 400,000 people attended the Las Vegas music event during its three-night run, the paper said.