That's the question pondered by police specialists who are now analysing the suspicious substance.
Stunned shoppers watched as fire crews with hazardous materials equipment, and police, converged on the CBD branch at the intersection of Grafton Street and Harbour Drive at 1.45pm.
Firefighters were greeted at the doors by the branch manager, who told them the powder had been discovered in an envelope which had been opened by a male customer in the presence of staff.
Emergency services taped off the immediate area.
Four employees who complained of itchiness to their faces and arms were isolated and taken into a room in the bank.
Firemen sealed off the rest of the bank and shut down the branch for the rest of the afternoon.
"We geared up in our spillage suits, and we decontaminated the four staff," Coffs Harbour Fire Station's officer-in-charge, Nat La Macchia, said.
Ambulance officers treated the four and took them to Coffs Harbour Health Campus as a precaution.
They examined seven more people at the scene, but they did not go to hospital.
Firefighters sealed up the substance and handed it over to police investigators.
It has been transported to Sydney for scientific analysis.
Up to 12 staff and three customers were in the bank at the time of the incident.