Premier promises to stop the Defqon.1 music festival after two deaths

The NSW Premier Gladys Berejiklian has expressed shocked over the deaths of two people after a music festival.

The NSW prime minister, Gladys Berejiklian, has agreed to stop the music festival of Sídq Defqon.1 after two young people died and two others were left fighting for their lives after multiple suspicions of overdose.

About 700 people were treated, including 18 who were hospitalized, during the event in Castlereagh, southwest of Sydney, on Saturday.

"I am absolutely horrified by what happened, I do not want any family to suffer the tragedy that some families are waking up this morning," he said.

"This is an unsafe event and I will do everything I can to make sure it never happens again."

A man, 23, and a woman, 21, collapsed at the festival around 9 pm on Saturday and died soon after at the nearby Nepean hospital, police said Sunday.

A woman from Jamisontown, 26, remains in critical condition at the Nepean hospital, while a man from Artarmon, 19, flew to Westmead Hospital and is in intensive care.

Police said another 18 people came to the hospital for drug-related problems, while about 700 people sought help from medical staff at the festival.

The organizers of Defqon.1 had warned ticket holders that the festival's drug policy was zero tolerance.

"This means that all types of soft and hard drugs are prohibited, if drugs are found, they will be handed over to the police," said a statement on the festival's website.

Police say 10 people were charged with drug offenses, including two 17-year-old girls who allegedly loaded 120 capsules "internally" at the scene.

In total, 69 people were found in possession of drugs at the festival held at the Sydney International Regatta Center.

Local detectives have formed a new police attack force, dubbed Highworth, to investigate the two deaths.