At least 70,000 people are being evacuated to enable the defusion of the World War (II) bomb in the Greek city.
It is said to be one of the largest mass evacuations over one of the largest wartime bombs to be found in Greece.
Officials could not tell if the bomb, which was discovered last week during road works, is German or an allied bomb
Residents within a radius of about 2 km of the bomb have however been compelled to evacuate the area between ahead of Sunday morning when the defusion is expected to take place.
About 1,000 police officers and 300 volunteers will be deployed ahead of the disposal operation.