Bomb disposal experts said the evacuation could wait until the weekend, adding there was no immediate danger.
The 1.8-tonne bomb, believed to have been dropped by British planes, was found at the building site in Frankfurt on Wednesday. The German media quotes the massive 4,000 pound bomb as having been given the nickname "Wohnblockknacker", or "Blockbuster" in English, during the war.
Currently, there is a police presence at the construction site, which has also been taped off.
German police will evacuate about 70,000 people from their homes on Sunday after an unexploded World War Two bomb was discovered in Frankfurt. It was found this week on Wismarer Strasse, about 2.5 kilometers (1.5 miles) north of the city's main shopping center.More news: JP Morgan Upgrades Rating On Palo Alto Networks, Inc. (PANW)
The evacuation will begin at 8:00 a.m. on Sunday, with the bomb disposal happening later that day and taking about four hours. In May 2017, another bomb, found in Hanover during pre-construction work on a building, forced another evacuation. Authorities issued a map with the evacuation zone that the bomb can damage.
The device is a British bomb, specifically a 1.4-ton HC 4000 air mine, the statement said, and is now under guard by police. Half were dropped on Germany, and an estimated 10 percent of those devices failed to detonate, according to Deutsche Welle.
The discovery of a World War II bomb is nothing unusual in Germany.