A flammable substance, possibly meant for use in a stage performance, exploded in midair at the Formosa Fun Coast water park in Taiwan on Saturday night, creating an immense fireball that injured at least 510 people, 183 of them badly enough to require intensive care at hospitals, according to CNN.

Eight of the injured were reportedly in critical condition as of Monday morning, while 43 were discharged with minor injuries. 13 of the injured are described as “foreign nationals” by AFP.

“Formosa Fun Coast indicated the fiery explosion occurred during a ‘Color Play Asia’ party put on by a separate marking company that leased out space at the park,” CNN reports.

Ambulance support was requested from surrounding cities to help with the injured, while the Taiwanese Defense Ministry put all of the military hospitals in northern Taiwan on alert to take patients from the water park. The injured are said to be scattered between 37 different hospitals, making it difficult to get an exact count. There were reports of people using rubber rafts and tubes from the water park as makeshift stretchers.

AFP describes the flammable substance as a multi-colored powder dropped over a thousand young people while they were dancing at a party. “But their joy turned to terror when the powder suddenly erupted into flames engulfing the partygoers in an inferno as they ran screaming for their lives,” said the report, noting that many of the kids caught in the explosion were clad in only swimwear.

“There was blood everywhere, including in the pool where lots of the injured were soaking themselves for relief from the pain,” said an eyewitness who described the scene as “hell.” His girlfriend added that she “saw lots of people whose skin was gone.”

The father of one victim wept over his daughter, who lies in intensive care with burns on 80 percent of her skin. “She was attending a music concert… why would there be an explosion?” he cried.

A health official explained that not only were their surface burns to the skin of the victims, but “there were also injuries caused by burns to the respiratory organs from the large amount of colour powder inhaled.”

Evidently, this sort of colored powder has been used safely on several previous occasions. It is not yet clear what set it ablaze this time. AFP reports that police are questioning five people, including event manager Lu Chung-chi, on “charges of offences against public safety and negligence of duties that caused severe injuries.”

Lu and one of his hardware technicians have been released on bail, but they are banned from leaving the country while the investigation continues. Unsurprisingly, the authorities have also banned similar “color party” events. The BBC notes that the Formosa Fun Coast Water Park, a booming business during the hot Taiwan summer, has also been shut down until further notice.

“Taiwan has suffered a series of deadly fires in the past couple of years due partly to poor enforcement of building and fire safety codes and illegal construction,” the BBC notes.