Teenager dies at Sydney dance party

A young woman found unconscious during a police drug raid at a Sydney dance festival has died.

More than five thousand people attended the dance party at Mrs Macquarie's Chair yesterday.

Officers were alerted to an unconscious 19-year-old woman as they carried out a drug operation at the event.

The Longueville woman was taken to hospital but later died, police said.

Officers, meanwhile, arrested 78 people at the event for drug offences.

Inspector Stewart Leggat of City Central Local Area Command warned about the dangers of taking illegal drugs, emphasising there was no quality control in their production.

"Quite simply, you don't know what you are getting - seeking a synthetic high, could result in a serious injury or death," he said.

"If you know of a business or person who may be involved in the sale of illegal synthetic substances, please contact Crime Stoppers immediately. We don't need to know who you are, all we need is the information you have.

"The information you provide could save someone's life."

Investigations into the woman's death are continuing.