Nine people have been hospitalised in Australia after taking drugs it is believed they mistook for cocaine.

The white powder substance was in fact hyoscine, which is commonly found in motion sickness medication.

Authorities were called to a house in Perth on Tuesday night and found several people in an unconscious or semi-conscious state.

Detectives were investigating if the cause of their condition was drug related.

They are all believed to be tourists, with Australian broadcaster ABC reporting that French and German citizens are among those hospitalised.

Dr David McCutcheon speaks to reporters at Royal Perth Hospital | Image: Facebook/Western Australia Police Force

Police say the prescription drug 'hyoscine' is the only identifiable drug detected in the samples tested from the house.

Dr David McCutcheon told reporters: "There was nine patients at this location - three of whom are still in a critical condition in ICU.

"They were brought to us in a state of agitated delirium, they were hallucinating, their hearts were racing, several of them have had to be put in a medically induced coma for their own protection.

"And I really need to emphasis how seriously unwell they were.

"It was very lucky there was someone on scene who could call an ambulance, because other wise their lives could have been put in danger."