Update 2pm Friday: While the Airport Post Office has reopened, the Customs Department within the building remains closed.
Customers will not be able to collect parcels that require duty to be accessed or payment of duty until Saturday.
Initial story: Police have removed what they described as “a suspicious substance” that was inside a mail bag at the Airport Post Office.
The substance will be tested by the Department of Environmental Health.
The mail bag, and the letters and packages contained within it, have been quarantined, police said, and staff members were decontaminated at the scene.
No-one was injured and there was no requirement for anyone to attend hospital.