The Jamberoo Post Office was shut down and the building evacuated after a package containing white powder was found on Thursday morning.
Staff at the post office alerted emergency services after discovering a suspicious package just after 9am.
Police, paramedics and firefighters all responded to the incident.
“When we got there we realised it was a white powder incident, so we’ve got standard operating procedures in how to respond to a job like that,” Inspector Peter Northey, from Lake Illawarra police, said.
“We immediately cordoned off the post office and evacuated everyone out of the building.”
Fire and Rescue NSW’s hazardous materials (HAZMAT) unit from Shellharbour was then called in.
Firefighters donned protective suits to enter the post office and retrieve the suspicious item, which was in a vacuum-sealed bag.
“It [the powder] actually hadn’t leaked out as we first thought,” Insp Northey said.
The package was sealed in a HAZMAT container and rushed to Sydney for forensic analysis.
The analysis has since determined the white powder was not suspicious, rather powered caffeine.
“At the time, we obviously didn’t know that,” Insp Northey said.
“The reason we were highly concerned at the time is the post office worker that opened the package said that her hands went all tingly, so that gave us concern.”
Inspector Northey said while the incident was deemed a “false alarm”, police still had to treat it as serious.
The worker, a woman believed to be aged in her 40s, was assessed by paramedics at the scene but did not require transport to hospital.
The post office was able to reopen when once the package was removed.