Twenty people were hospitalised and 40 arrested at the Electric Parade dance music festival at the Sidney Myer Music Bowl on Saturday night.

Ambulance Victoria state health commander Paul Holman said the festival was "awash with drugs".

Of those arrested, 28 people received diversions and two received cannabis cautions.
 
One man was charged and remanded after being found with quantities of ecstasy, cocaine, MDMA, LSD, ketamine and hashish.

Ambulance Victoria treated 25 people at the festival , with 22 taken to hospital, many in a critical condition.

It is believed they had overdosed on the synthetic drug GHB. Paramedic callouts began about 6pm.

A spokeswoman for St Vincent's Hospital said parents had been calling its switchboard on Sunday morning looking for their children.

Ambulance Victoria spokesman John Mullen said another eight people had been treated for drug overdose at the White Night festival.

Paramedics treated 46 people at the event for various conditions, with 17 taken to hospital.

"It would appear we've had a significant amount of drugs at the party at the Sidney Myer Music Bowl," he said.

"We've transported 22 people from that event alone, and we're now up to 30-plus from that event and across the city, all with GHB overdoses, all critically ill."

Mr Holman said GHB slowed the heart rate and could cause people to become unconscious or have seizures.

He said the "deeply unconscious" patients had been taken to three hospitals: St Vincent's, Royal Melbourne and The Alfred.

"Paramedics treated seven other people who left the event and collapsed in nearby parks and streets," Mr Holman said.

A Royal Melbourne spokeswoman said the hospital had received four patients and only one remained in hospital, in a stable condition.

The Alfred received 15 patients, but a spokeswoman said it was not known if all of them had come from the Electric Parade festival.

Two remained at The Alfred in a stable condition on Sunday night.

A spokeswoman at St Vincent's said the hospital had received eight patients, and only one remained in the emergency department for observation.

She said it was unusual to have such a rush of people who had overdosed coming in on a Saturday night.

Professor George Braitberg, director, Royal Melbourne Hospital, said recovery was often "fairly brisk".

"What it does is ... it suppresses the central nervous system ...if your respiratory centre, if that is depressed, you slow down your breathing and eventually you stop breathing," Professor Braitberg said.

"The treatment is really observation and wait for the drug to be metabolised out of the brain, which usually takes six to eight hours."

He said the most likely cause of the overdose was a potent batch.

"The biggest problem is you don't know what they are being made with, but it could also be a question of potency," Professor Braitberg said.

"It may just have been a really strong ...batch."

More than 40 paramedics had been stationed in the CBD to help with White Night celebrations.

"A lot of those vehicles were used at the Sidney Myer Music Bowl; it was a significant impact on our resourcing right across the area – particularly sad seeing as it's all preventable," Mr Holman said.

"This is particularly disappointing on a night where Melbourne is out enjoying itself and really that event [Electric Parade] was awash with drugs."

Electric Parade billed itself as "Your chance to experience amazement and bliss".

"As the sun sets, you are left dancing to the pulsating sounds of the world's greatest international DJs and live acts. Electric Parade - Expect the unexpected!"

The event headed north to the University of Sydney on Sunday.

Festival-goer Ben Farrow said he was very upset to see so many people had overdosed at the festival.

"I noticed at the end a lot of ambulances ... they seem to be working ... more than normal," Mr Farrow said.

"At least three or four all leaving at the same time."

Although it was his first time at Electric Parade, Mr Farrow, 36, said he had been going to such festivals since he was 20.

But the professional chef, who was at the event with six other friends, said such incidents gave the music festival a "negative spin".

"I am a bit old-school. I purely go for the music and I just dance," Mr Farrow said.

"GHB, especially, I am not a fan of at all. It really gives the whole techno scene a bad name.

"I know it is happening. It upsets me, and it is not a good part of the night."

Another attendee, known as Straw, had been selling clothes at the event with his friends.

He said it was obvious who was taking GHB.

"The way they sway, the way they look - they're not really conscious," he told Channel Nine.

Earlier this month, three people died and up to 20 people were hospitalised after taking a deadly batch of ecstasy.

Most of it occurred around the Chapel Street precinct.

It later emerged that the police knew about a toxic batch of drugs being sold in Melbourne's nightclubs, but failed to warn the public.

Assistant Commissioner Stephen Leane said it was too early to tell if the drugs found this weekend were linked to any previous overdose events.

Police will speak with the organisers about the future of the festival, he said.

"They need to reach a standard where they can get access to another venue," he said.

"And that's a question we'll be asking them next week: whether they've done everything they can if they want to run another one, and whether they should be allowed access to a venue to run an event like that."

Event organisers have been contacted for comment.