Police evacuated an area in the heart of Berlin on Friday that includes the central train station, the Economy Ministry and a major museum as bomb disposal experts prepared to defuse a World War Two bomb.
German rail operator Deutsche Bahn said it expected long-distance train transport at the central station to be disrupted from 10 am to 2 pm local time. It said trains would stop at other stations in Berlin instead.
Buses, trams and local train services in Berlin were also disrupted and the road where the 500-kilogram British bomb was discovered during building work this week was closed.
Police began evacuating all buildings within an 800 metre radius of the bomb at 9 am.
They posted a video on Twitter showing officers walking up the stairs in an apartment building with the caption: "We're not bringing room service or breakfast in bed but a personal wake-up call ... Residents are being asked to leave their homes due to the bomb from the World War being defused."
The evacuation area also includes the Natural History Museum.
Flights from Berlin's Tegel airport are due to go ahead as planned but the capital's airport operator warned passengers on Twitter that public transport to the city's two airports - Tegel and Schoenefeld - would be affected.
More than seven decades after the end of World War Two, Germany still discovers more than 2,000 tonnes of live bombs and munitions every year.
Last year some 60,000 people were evacuated from their homes in Frankfurt after a massive bomb dropped by Britain's Royal Air Force was unearthed.