German police began evacuating thousands of people around Berlin's central railway station on Friday, as bomb disposal experts prepare to move in to defuse an unexploded World War II explosive unearthed on a building site.
Trains, trams and buses were halted or rerouted as police using a van-mounted loud-hailer announced the operation to dispose of the British 500-kilogramme (1,100-pound) bomb found more than 70 years after the war.
Authorities have declared an exclusion zone with an 800-metre (yard) radius around the site located just north of the central railway station, a transport hub that on a normal day is used by 300,000 passengers.
Arriving from Leipzig on a day trip to Berlin, Japanese tourist Yamamoto looked bewildered as he was told of the operation at the railway station.
"We didn't know anything about the bomb," he told AFP.
The exclusion zone covers the train station, an army hospital, the economy ministry, an art gallery and a museum as well as part of the BND intelligence service's new headquarters.
Many thousands of residents and employees will also have to stay clear of the area and not return until police give the all-clear.
Before the bomb disposal experts move in, police will go house to house to check the zone has been completely cleared.
Temporary shelters have also been set up for those affected by the evacuation.
Angela Merkel's chancellery building and the Reichstag (parliament) lie just a few hundred metres to the south of the no-go zone and can keep operating as usual.
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.
In the biggest post-war evacuation, at least 60,000 Frankfurt residents were forced to leave their homes last September so that an unexploded 1.8-tonne British bomb dubbed the "blockbuster" could be defused.
Some 3,000 such unexploded bombs are believed to still lie buried in Berlin, a city of three million people, where disposal squads are well-practised in defusing them and other ordnance.
It was unclear how long the bomb disposal squad would take to disable the bomb found during construction work on Heidestrasse in the district of Mitte.
"It depends on how long the evacuation takes and of course the condition of the bomb," police spokesman Martin Halweg told the Tagesspiegel daily.
Police have asked residents to stay with family or friends or head to one of two emergency shelters set up at nearby schools.
They said the bomb was "safe for now", reassuring nearby residents that "there is no immediate danger".
Urban transport operators prepared for large-scale disruptions around the central hub.
Trains were running straight through the central railway station without stopping from 0800 GMT, and all rail traffic there will cease from 0930 GMT, operator Deutsche Bahn said.