The woman who died at Stereosonic reportedly took a mix of ecstasy and MDMA mixed together in a bottle of water which led to her death.

Sylvia Choi, 25, was a qualified pharmacist from Oyster Bay and collapsed just minutes after taking the drug concoction at Stereosonic music festival at Sydney's Olympic Park.

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Sylvia Choi, 25, went into cardiac arrest after taking the drug concotion. Photo: NSW Police

The young woman went into cardiac arrest after taking the deadly mixture and later died at Concord Hospital at 9.30 on Saturday night, say reports.

Ms Choi’s school friend Aimee Herbert told Daily Mail Sylvia was a smart girl who would ‘go far in life’.

“She was a talented and amazingly kind girl and I cannot believe that this would ever happen to her,” she said.

“It's such a waste of a beautiful life.”

Ms Choi graduated school at Gymea Technology High School in 2007 and studied at the University of Sydney before beginning her career as a pharmacist.

“I went to school with Sylvia. I cannot comprehend this. She was amazing and so smart and talented and I am in utter shock. Rest In Peace, Sylvo,” Ms Herbert said.

Phil Smith, the CEO of Blooms The Chemist said in a statement Ms Choi was ‘one of our bright, well-respected and highly professional pharmacists’.

“We extend our deepest condolences to Ms Choi’s family and ask the broader community to respect their privacy during this difficult time,” he said.

A friend staying with the family told Daily Mail Ms Choi's parents and siblings were very distressed over her death.

The tragedy comes as another woman was placed in an induced coma on Saturday after attending the festival.

A 22-year-old woman from the UK was taken to Westmead Hospital in a critical condition.

It was announced on Sunday morning that her condition had been upgraded to stable.

A further nine people were taken to hospital for treatment and later discharged.

Meanwhile, 69 people were charged with with possessing and supplying drugs, a number police said was "alarming and disappointing".

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Thousands swarmed Sydney's Olympic Park for the Stereosonic music festival on Saturday. Photo: Twitter/Rachael MadiganSmith

South West Assistant Commissioner Frank Mennilli said the message doesn't see to get through to some people.

"These drugs are made by criminals in back yards," Mr Menilli said, according to The Daily Telegraph.

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