The 100-kilogramme explosive was unearthed on a building site adjacent to the Alexa shopping centre at the central transport hub of Alexanderplatz in the city's east.
People were being evacuated from within a 300-metre (1,000-feet) radius of the corroded bomb, which had an intact detonator, police said.
It was expected that a bomb disposal squad would attempt to defuse the device later in the day on Friday. On Twitter police warned that nearby areas would remain blocked off.
Die #Weltkriegsbombe in #Mitte muss noch heute vor Ort entschärft werden. Unsere Kolleg. treffen zzt. die nötigen Vorbereitungen. Rechnen Sie damit, dass es im Umkreis des Fundortes bis in die Nacht zu Sperrungen kommt.
Weitere Infos folgen hier. https://t.co/wiu0HUhgj2
— Polizei Berlin Einsatz (@PolizeiBerlin_E) June 14, 2019
The bomb find was expected to cause traffic problems on Friday evening and night, including on the S-Bahn lines S3, S5, S7 and S9 between Alexanderplatz and Ostbahnhof.
Im Bereich #Alexanderplatz wurde eine Weltkriegsbombe gefunden, die Entschärfung soll in den Abend-/Nachtstunden erfolgen. Voraussichtlich werden die Linien #S3, #S5, #S7, #S9 Alexanderplatz #Ostbahnhof unterbrochen, weitere Infos dazu folgen. https://t.co/6DzmAfcCTJ pic.twitter.com/LHLgwjH2GM
— S-Bahn Berlin (@SBahnBerlin) June 14, 2019
Almost 75 years after the end of World War II, Germany remains littered with unexploded ordnance, a legacy of the intense Allied bombing campaign against Nazi Germany.
Berlin was subject to a campaign of intense bombardment during the war, particularly in the spring of 1945, with a third of the city's homes destroyed and tens of thousands of people killed.
According to information from the local government released in April, there are still about 4,600 unexploded World War II bombs in Berlin.
Over the past two years, twelve bombs heavier than 50 kilos have been found in Berlin.
In the last few days, bomb squads defused two WWII bombs in Oranienburg, Brandenburg. Meanwhile, a bomb was defused in the Hermsdorf area of Berlin in May. Since parts of the S-Bahn lay within the restricted area, the company reported “massive traffic disruptions”.
In April 2018, Berlin police defused a 500 kilogramme British bomb, forcing the evacuation of 10,000 people.
In the biggest post-war evacuation to date, some 60,000 Frankfurt residents were evacuated in 2017 so that an unexploded 1.8-tonne British bomb dubbed the “blockbuster” could be defused.