The order went out early on Friday morning for thousands to be evacuated from central Lublin, a day after a construction worker uncovered an unexploded 550-pound bomb during ground excavation.
Some 14,000 people were moved, many of them by buses to a local stadium, with special provisions made for local kindergartens and for disabled people requiring care.
Lublin Mayor Krzysztof Żuk told Polish media that a crisis team had been assembled after the bomb was discovered.
"All our units are ready and cooperating closely with the police and army as well as the Fire Brigade, all the services responsible for the whole process of making the ordnance safe and disposing of it," Żuk said, adding that the situation was "under full control."
According to local media, the bomb had fallen on the site of a pre-World War II aircraft factory which became part of the Majdanek concentration camp after Nazi Germany occupied the area in 1939.