HUNDREDS of workers have been evacuated from an Australian Taxation Office (ATO) building in Sydney's west after a letter containing suspicious powder was received.
The letter was opened in the mailroom of the Penrith premises about 8.20am (AEST) on Thursday, police said.
An unidentified powder was found inside the envelope, prompting employees to raise the alarm.
More than 800 workers were evacuated from the building and mailroom staff were quarantined.
Police, ambulance and a Hazmat team from the NSW Fire Brigades attended the scene.
A fire brigades spokesman said later the mailroom employees had shown no signs of illness.
Forensic teams had not yet determined what the powder was but employees were allowed to return to work.