The Electric Zoo music festival was canceled Sunday after two people died in the first two days of the dance music party in New York City, the promoters said.

Both people who died overdosed on drugs, possibly MDMA or ecstasy, according to the New York Police Department. Four other people became critically ill and were hospitalized in intensive care, police said.

"The City recommended cancellation and the event promoters have agreed," the NYPD and Mayor Michael Bloomberg's office said in a joint statement. "The Electric Zoo organizers have worked with City officials to reduce health risks at this event, but in view of these occurrences, the safest course is to cancel the remaining day of the event."

City health officials were trying today to determine whether the drugs in circulation at the festival were an especially potent batch, whether they had been poisoned, or whether the deaths and illnesses were caused by people using drugs they were not used to in heat and humidity, without eating or drinking.

The cancellation was announced in a brief statement on the festival website.

"The founders of Electric Zoo send our deepest condolences to the families of the two people who passed away this weekend," the statement said. "Because there is nothing more important to us than our patrons, we have decided in consultation with the New York City Parks Department that there will be no show today."

The festival, which takes place on New York's Randall's Island, has been held since 2009.

Among the big names at this year's event were Avicii, David Guetta and Diplo. Scheduled to perform Sunday were DJs Armin Van Buuren, Sebastiona Ingrosso, Steve Aoki and Laidback Luke.