Eight of the nine were in a critical condition and had been put on breathing tubes after falling unwell on Saturday, Ambulance Victoria director Vanessa Gorman told AAP.

She could not confirm which drugs were consumed but said seven people inside and two outside the venue fell unwell over a period of several hours.

Victorian Ambulance Union secretary Danny Hill believes the overdoses are down to a particularly bad batch of MDMA circulating in the community.

“I don’t think we’ve seen this amount of people in one event become so critically unwell that they needed to be placed into an induced coma,” Mr Hill told AAP.

“We have a lot of people very, very sick.

“There’s always side effects to drugs but this would have to be one of the worst that we’ve seen as far as people being so critically unwell at one event.”

Mr Hill said patients were unconscious and having seizures as their heart rate, blood pressure and temperature skyrocketed.

He said one person had a temperature of 41C, which is well above normal levels.

The patients were taken to Sunshine Hospital, Royal Melbourne Hospital, The Austin Hospital, Footscray Hospital and St Vincent’s Hospital.

Ms Gorman said warm weather and heat created by thousands of people dancing at the Hardmission festival could have exacerbated their condition.

The union believes the incident highlighted the need for pill testing at festivals not only to inform potential drug users about what they would be taking but also help emergency services allocate resources.

“It gives an option for people who are concerned about what they might be taking to check it and if they find out that it’s the deadly substance that put eight people in hospital the week before then maybe they’re not going to take it,” Mr Hill said.

“These drugs are not made in batches of seven or eight, they’ll be hundreds if not thousands of these exact same tablets out there today and many more music festivals coming up over the summer season.

“It’s terrifying to think that this exact same drug might cause the exact same outcome for other partygoers.”

Victoria Police confirmed an investigation was underway into reports people became unwell and had to be taken to hospital while attending the festival.

A spokesperson said officers were not aware of any critical health incidents at the time but were now making inquiries.

AAP has contacted Hardmission Events for comment.