Several government ministries, the German Intelligence Service, a courthouse and the Museum for Contemporary Art fall within the zone and were closed.
Undetonated World War II bombs are frequently discovered in Germany, especially during construction projects, prompting disposal operations that often involve large-scale evacuations.
The main problem could be the transport, because it will have to close for a few hours the main station of the capital from 10 am (no walk trains, trains, metro and buses within a radius of 800 m).
More than 70 years after the end of the war, unexploded bombs are regularly found, a potentially deadly legacy of the intense Allied bombing campaign against Nazi Germany. "The detonator has been blown off in a controlled explosion", said Berlin police on Twitter, adding "#Goodjob guys".
USA wildfires leave two dead in Oklahoma
Temperatures are projected to reach the mid-90s with humidity below 10 percent and winds gusting to 40 miles per hour (64 kph). Days after a fire ravaged the small town of Martha, cleanup continues, along with efforts to help victims recover.
The police say there is no immediate danger from the 500 kg British bomb, which was found on Heidestrasse last Wednesday. Many thousands of residents and employees will have to stay clear of, or leave the area by 9:00 am local time (0700 GMT), and not return until the bomb is safely defused.
The deactivation of the bomb is scheduled to begin at 11.30am but it is not known how long it will take.
Flights from Berlin's Tegel airport are not affected but passengers have been warned that public transport to the city's two airports - Tegel and Schoenefeld - would be disrupted.
Unexploded bombs are so prevalent that the city offers a free service to landowners who are seeking to build: a team of researchers will examine old aerial photos and data to determine whether a property may have once been bombed.