Hospital staff and patients were alerted to the fire just after 5pm, with around 200 patients from a six storey block of the building evacuated room by room and led into carparks outside.

Patients were wheeled out in beds and wheelchairs, with some still attached to IV drips as they waited for smoke to clear inside the hospital.

Patients about to give birth or requiring emergency care were transferred to nearby hospitals in ambulances under police escort following the evacuation. At least four fire crews attended the scene and extinguished the blaze before it could spread to other parts of the hospital.

A FESA spokesman said the fire had burnt through paper and cardboard in one of the hospital's laboratories. Authorities are yet to determine the cause of the blaze.

Police and fire crews have closed off all roads surrounding the hospital, including Bagot Rd, Railway Rd and Barker Rd. Perth Fire Station district manager Brad Delavale said patients had been removed from the hospital block as a precautionary measure. "We evacuated everyone because of the amounts of smoke that were coming into the building, and we are in the process of removing that smoke from the building."