A teenager has died and three other people were taken to hospital in a critical condition from suspected drug overdoses at a music festival in Sydney's inner west.

Key points: Knockout Games of Destiny is touted as the biggest indoor festival in the southern hemisphere

Knockout Games of Destiny is touted as the biggest indoor festival in the southern hemisphere The NSW Government has refused to introduce pill testing, despite growing pressure

The NSW Government has refused to introduce pill testing, despite growing pressure It introduced tougher drug supply and possession laws after two deaths at the Defqon.1 festival in September

Police say the 19-year-old man died in Concord Hospital after attending Knockout Games of Destiny — billed as the biggest indoor festival in the southern hemisphere — at Sydney Olympic Park on Saturday.

The man, from Baulkham Hills in north west Sydney, was found at a train station near the event.

Two women, aged 19 and 25, and a man were taken to Westmead Hospital in a critical but stable condition.

Two patients had woken up from induced comas on Sunday and a hospital spokesperson all three patients were in a stable condition in hospital.

Thirteen other people were also taken to hospital for treatment and more than 100 were treated for various conditions during the event.

It follows the deaths of two partygoers at the Defqon.1 festival in September.

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Officers said an 18-year-old woman was allegedly found with almost 400 MDMA caps and was charged with supplying a prohibited drug.

Four other people were also charged with drug supply offences.

South West Metropolitan Region Commander Assistant Commissioner Peter Thurtell said many festival-goers were choosing to ignore warnings about illicit drugs.

"There is no acceptable use for drugs — the message is clear," he said.

"We will continue to have a strong presence at festivals and dance parties with the wellbeing and safety of attendees our number one priority."

Officers from Auburn Police Area Command are investigating the circumstances surrounding the man's death and a report will be prepared for the coroner.

Pill testing not on the table

NSW Premier Gladys Berejiklian extended her condolences to the teenager's family, but said her government would not change its stance on pill testing.

"Unfortunately we know that pill testing won't work because it will give people the green light to taking substances which in the end could still kill them," she said.

"Everybody's body is made up differently, everybody responds to chemicals and substances in a different way — pill testing doesn't mean it's safe.

"I would hate to think that even after something has been tested that somebody dies."

The NSW Government introduced tougher drug penalties in October — including on-the-spot fines for drug possession and a maximum 20-year jail sentence for drug suppliers — following the Defqon.1 deaths.

Ms Berejiklian said she wanted young people to have fun without taking illegal substances.

"I'm beside myself that young people aren't getting the message," she said.

"This is a serious issue."

An 18-year-old man died at a Knockout music event last year, after he tripped over and fell on his head.