On Saturday night, an explosion onstage at a concert at Formosa Water Park, in New Taipei City, in Taiwan, started a fire that spread into the crowd, injuring at least 500 people, the Associated Press reports.

Wang Wei-sheng, a spokesperson for the New Taipei City fire department command center, told the AP that an accidental explosion of an unknown powder was the initial catalyst for the fire.

It was not clear whether the powder, which witnesses said was blown into the air, was part of the performance. There were around 1,000 spectators at the concert.

According to Taiwan’s Central News Agency, the fire was quickly brought under control. Victims were brought to the Mackay Memorial Hospital in Tamsui, the Chang Kung Memorial Hospital in Linkou and the Taipei Veterans General Hospital in Tienmu, Taipei City, for emergency treatment. Several reportedly had burns over 40 percent of their bodies.

CNN reports that Mayor Eric Chu called the event the “worst incident of mass injury (ever) in New Taipei.” New Taipai is Taiwan’s most populous city.

Update, 6/28 – On Sunday morning, the toll of those injured in Saturday’s explosion reached 516 people, the New York Times reports. More details emerged surrounding the circumstances of the explosion:

The public’s focus immediately turned attention to the colored powder — what the organizer claimed on its Facebook page to be cornstarch mixed with food coloring — that was sprayed at high velocity on revelers from a stage. Many people asked how, if it was flammable, the mixture was allowed to be used at such events, several of which have taken place in Taiwan in recent years.

Among the victims were four mainland Chinese and two foreigners, the AP reports. An 18-year-old from Taiwan had burns over 90 percent of her body.

“I apologize to all the families,” the event’s organizer, Lu Zhongji, who was taken into custody with two others for questioning, said. “I accept full responsibility for this.” CNA reported that several people may be charged with negligence and public endangerment.

Photo credit: AP Images. Contact the author of this post: brendan.oconnor@gawker.com.