German authorities are set to evacuate more than 60,000 people from the center of Frankfurt this weekend.
Airspace for 1.5 kilometers around the bomb site will also be closed.
Officers are guarding the site and say there "is now no danger". All work on the site has stopped, and the bomb is covered under a blue tarp. According to the local newspapers, police fears that nearly 70,000 people can be affected.
One of the biggest such evacuations to date took place last Christmas, when another unexploded British bomb forced 54,000 people out of their homes in the southern city of Augsburg. More recently, in May, about 50,000 people in Hannover had to leave their homes. According to a press release from the Frankfurt fire department, the bomb is a "blockbuster" bomb of a type usually dropped by British Royal Air Force bombers.
Officials said the bomb contains 1.4 tons of explosives.
The bomb will be defused following the evacuation on Sunday, the press release said.
It is reportedly unclear if any flights would be interrupted on Sunday at Frankfurt airport, which is Germany's largest, and this will likely depend on the prevailing wind conditions that day.
Roads and transport systems, including the underground, will be closed during the work and for at least two hours after the bomb is defused, to allow patients to be transported back to hospitals without traffic.