Police and paramedics were called to the festival at Mrs Macquarie's Chair, on Sydney Harbour, about 4.40pm on Saturday, after reports of an unconcious woman.

The 19-year-old from Longueville was taken to St Vincent's Hospital, where she later died.

More than 5000 people attended Harbourlife, and 78 people were arrested for drug offences. Police later issued a warning about the dangers of taking illegal drugs.

"There's little to no quality control in the production of illicit drugs," Inspector Stewart Leggat of City Central Local Area Command said. "Quite simply, you don't know what you are getting – seeking a synthetic high, could result in a serious injury or death.

"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."

Harbourlife is an annual outdoor dance festival, which hosts international DJs, and is promoted as being "one of Sydney's most loved music events".

Police investigations into the woman's death are continuing, and a report will be prepared for the coroner.

Fairfax Media