The New South Wales premier, Gladys Berejiklian, has vowed to stop the Sydney music festival Defqon.1 after two young people died and another three were left fighting for their lives after multiple suspected overdoses.

A man, 23, and a woman, 21, collapsed at the festival in Castlereagh about 9pm on Saturday and died a short time later in nearby Nepean hospital, police said on Sunday.

The three who are critically ill include a Jamisontown woman, 26, who is at Nepean hospital, and an Artarmon man, 19, who was flown to Westmead hospital and is in intensive care. Another man is in a critical condition at Liverpool hospital.

Police said another 13 people went to hospital for drug-related issues while about 700 people sought assistance from medical staff at the festival.

A range of illicit drugs were seized including MDMA, cocaine and ecstasy.

Defqon.1 organisers had warned ticket holders the festival’s drug policy was zero tolerance.

“This means that all types of soft- and hard drugs are prohibited. If drugs are found, you will be handed over to the police,” a statement on the festival’s website said.

Police say 10 people were charged with drug supply offences, including two 17-year-old girls who allegedly carried 120 capsules “internally” into the venue.

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

The police have formed a new strikeforce, Highworth, to investigate the deaths.

Berejiklian said she was “absolutely aghast” at what had occurred.

“I don’t want any family to go through the tragedy that some families are waking up to this morning,” she said. “This is an unsafe event and I’ll be doing everything I can to make sure it never happens again.”

The police urge anyone with information about this incident to contact Crime Stoppers: 1800 333 000 or nsw.crimestoppers.com.au.