"There're still people surfacing, and they need to be brought out of the evacuation zone", said a spokesman for Frankfurt's firefighting service, adding that this process was "incredibly annoying and time-consuming".
The bomb was found during work Tuesday close to the Goethe University Frankfurt compound, police said in a statement.
As well as residents, more than 100 hospital patients from Frankfurt and Koblenz, including premature infants and those in intensive care, have also had to be moved to safety.More news: Colts Add QB In Trade With Patriots
Bomb technicians had been scheduled to begin work shortly after noon, but the fire department said there were delays as some people refused to leave. We will now assess if everybody has left voluntarily and go from house to house and remove people if necessary. Officials said it would take four hours to disarm the bomb.
Three police explosives experts in Goettingen were killed in 2010 while preparing to defuse a 1,000 lb (450kg) bomb. "I have never seen anything like it".
"Not everyone has the opportunity to spend the day with friends or relatives".More news: US Job Growth Slower But Still Strong in August
Frankfurt airport tweeted that airport tours would be free to all Frankfurters forced to leave their homes, while residents organized other distractions such as yoga in the park.
Similar operations are still common 72 years after the war ended.
More than 60,000 people have been ordered to leave a radius of 1.5 kilometers - almost a mile - around the site where the 1.8-ton British bomb will be disposed of Sunday.More news: Japan, South Korea agree to seek stronger United Nations resolution against N. Korea
The bomb was found during construction in an upscale area.