Nine people have been taken to hospital after suffering suspected drug overdoses at a music festival at Flemington Racecourse in Melbourne.

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 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."

He 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 ambulance 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 to 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."

Victorian minister Steve Dimopoulos said the government has no plans to introduce pill testing and was focused on harm minimisation.

He said poison authorities were still working out exactly what happened including whether there was something in the pills or people had a reaction.

Coalition spokesman David Davis told reporters the opposition does not support pill testing.

But upper house cross benchers Legalise Cannabis, the Greens and Animal Justice Party say the Flemington incident shows why Victoria should follow the lead of ACT and introduce the measure over concerns young people could die.

Victoria Police confirmed it was investigating reports of people becoming unwell at the festival.

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

AAP has contacted Hardmission Events for comment.