The bomb squad is reportedly investigating an explosive device that was found at an electricity substation in western Sydney.
Workers at the Kingswood substation on Smith Street found what is believed to be a petrol bomb with a detonator shortly before 9am on Thursday, The Daily Telegraph reports.
Police have confirmed an operation is under way.
Nearby Nepean Hospital told AAP it was not evacuating but was taking advice from NSW Police.
The nearby Kingswood South Public School remains open.