Two people are fighting for their lives in intensive care and seven others were taken to hospital after a suspected mass drug overdose at a Perth property, with witnesses describing how people suffering "seizures" were taken away on stretchers.

Those affected are believed to be backpackers or students living at the property, which is in the inner Perth suburb of Victoria Park.

There were five French citizens aged from 21 to 24, two Germans aged 21 and 22, a 25-year-old Italian citizen and a 24-year-old from Morocco, police revealed.

Emergency services were called to the Colombo Street home just before midnight after reports nine people were unconscious or violently ill.

Seven men and two women were rushed to three separate hospitals around the city.

Two remain in intensive care.

Sorry, this video has expired Perth police on scene of suspected mass overdose

Royal Perth Hospital emergency medical physician David McCutcheon said several patients had to be put into induced comas.

"They were brought to us in a state of agitated delirium, they were hallucinating, their hearts were racing," Dr McCutcheon said.

"Several of them have had to be put in a medically-induced coma for their own protection.

"I really need to emphasise how seriously unwell they were."

'Some of those patients would have died'

RPH clinical toxicologist Jessamine Soderstrom said some patients would likely stay in induced comas for days.

She said it was "extremely lucky" an ambulance was called when it was.

"If it wasn't timely call of the resident ... some of those patients inevitably would have died," she said.

"When your body overheats to a certain temperature for a certain period of time it's like cooking an egg.

"Your proteins basically denature and you go in to multi-organ failure and patients die from that."

A man arrives back at the house after being released from hospital. ( ABC News: James Carmody )

The drugs have been sent to the WA ChemCentre for analysis, but authorities are not yet able to say what substance caused the reaction.

Two students, from Germany and Colombia, have told the ABC they were not involved in the incident, but were shocked to find out what had happened when they returned to the house last night.

Organised Crime has been notified due to the presence of drugs, police said.

People 'having seizures' while being stretchered out of house

After hearing noises, local resident Sebastian Arevalo went outside to find eight ambulances and at least six police cars on the street.

"It was just absolutely crazy. People were rushing around, rushing into the house … it was really, really scary," he said.

"And people just started coming out in stretchers, most of them were in like an unconscious state, but one of them was kicking and having almost like a spasm."

His partner Sophie Barnet said the whole episode was terrifying to watch.

Sebastian Arevalo said it was very scary watching the events unfold. ( ABC News: Graeme Powell )

"They [the stretchers] were all coming past in a line it was so scary and they had glassed eyes and they were like in a different world it was so scary to look at … a lot of them were having seizures," she said.

"A lot of them were shaking and trying to get out of the bed, but I don't think they knew they were doing it.

"And there was one guy that was really violent on the stretcher, he was like punching the air and everything."

'It's like a backpackers' hostel'

Mr Arevalo said a lot of backpackers stay at the house.

The couple said ambulances and police were called to the house last weekend, but they did not see anyone being taken away.

Ambulances were called to the Colombo Street house just before midnight. ( ABC News: James Carmody )

Neighbour Garry Baden-Davidson said it was common to see different people staying at the property.

"It's like a backpackers' [hostel], they come and go. For two weeks, one lot will come and then another lot will go out," he said.

Another neighbour, Mark, also witnessed the incident and said there had been problems at the house previously.

"The kids who were still with it were sort of upset and crying and carrying on with all the policemen, but they were all obviously from overseas," he said.

"My brother-in-law Tim, who owns the place [next door], he's had contact with them [the property owners] before because they're Chinese people with too many people staying here.

"They've had problems with backpackers before."

The ABC saw multiple mattresses crammed in on the floor of the house.

Town of Victoria Park Mayor Trevor Vaughan said in a statement the property had been investigated in June 2016 after complaints it was being used for short-term accommodation without approval.

The owners were told to stop using the property in that way, and they complied.

However Mr Vaughan said since the incident last night, they would be again investigating the use of the property.

The council said it had received no complaints about other properties owned by the same couple in the area.