The WA Police Bomb Squad remain at the scene of a chemical incident near Sir Charles Gairdner Hospital.
The incident was reported just after 11.30am.
Police say it appears an unstable chemical was stored at a facility located in an outbuilding of the hospital.
"The immediate area is being evacuated, police are assessing. Police can advise that no patients are affected," a police briefing note said.
The Bomb Squad are at the scene assessing the situation.
In a statement the North Metropolitan Health Service said "selected laboratory and office buildings located on the QEII Medical Centre site were evacuated as a precaution after an unstable legacy chemical product was found in a laboratory that was being cleaned out."
"No patients were affected as a result of the precautionary evacuation, and Sir Charles Gairdner Hospital continued to operate as normal throughout," the statement said.
"The product was quickly contained and the situation continues to be managed by emergency service personnel.
"As a result of today's incident, it is planned for additional audits of QEII Medical Centre buildings to be undertaken."
