About 65,000 Frankfurt residents have left their homes for the day to allow experts to defuse a massive unexploded bomb from World War Two.
It has been described by local media as the biggest such evacuation in post-war German history.
Police checked every designated house with heat-detection technology to make sure everyone was out.
The evacuation area in the Westend district includes hospitals, nursing homes and Germany's central bank.
There are believed to be hundreds of thousands of unexploded wartime bombs across Germany.Image copyright Reuters Image caption Streets were closed off by police early on Sunday morning Image copyright Reuters Image caption Police helicopters carrying heat detecting cameras scoured the area as bomb disposal experts began their task
Police on Sunday cordoned off the 1.5km (1 mile) evacuation area as residents carrying luggage vacated the danger zone. A few stragglers who were slow to move may be prosecuted, local media reported.
Many residents said they were going to make the most of the day either by visiting relatives or enjoying a day out in a different part of the city until it is safe to return home in the early evening.
Police told local media that the evacuation is roughly on schedule and that everyone has now been moved from the danger area.
The 1.4 tonne British bomb was found on a building site on Wednesday.
More than 100 patients from two hospitals were moved on Saturday including premature babies and people in intensive care. Some care home residents left early on Sunday.
Fire and police chiefs in the city warned that an uncontrolled explosion of the HC 4000 bomb would be powerful enough to flatten an entire street.Image copyright AFP Image caption Residents can stay in makeshift shelters while the bomb disposal process is under way Image copyright EPA Image caption The site where the bomb is waiting for explosion has become a draw for locals and tourists
The bomb disposal operation is expected to take about 12 hours.
Police helicopters carrying heat detecting cameras scoured the area as bomb disposal experts began their task. Police are guarding empty houses and apartments from burglars.
The evacuation area includes 20 retirement homes, an opera house, and Germany's central bank where half the country's gold reserves are stored.
The city has opened shelters for evacuees to spend the day, and most museums are opening their doors for free.
A smaller evacuation took place on Saturday in Koblenz, about 110km (68 miles) west of Frankfurt, while experts disposed of a World War Two bomb that had been found during the construction of a new kindergarten.
So, how many unexploded bombs are there in Germany?
An average of about 2,000 tonnes of unexploded ordnance are found each year in Germany. It's estimated that about half the 2.7 million tonnes of bombs dropped by Allied powers during World War Two landed on German soil (compared to about 74,000 tonnes of bombs dropped on the UK by Germany). Many of the bombs were equipped with malfunctioning time-delay fuses, and many never went off.
Adding to the problem are Russian artillery shells, German hand grenades and tank mines, as well as Russian munitions from training facilities in post-war East Germany.
The problem is so widespread that Germany has a bomb-disposal unit, the Kampfmittelbeseitigungsdienst (KMBD), dedicated to the problem. Its technicians are among the busiest in the world, deactivating a bomb every two weeks or so - and they estimate their work will continue for decades to come.
Do the bombs pose a real threat?
Dozens of bomb-disposal technicians and hundreds of civilians died from uncontrolled explosions in the decades following the war. The rate of fatalities has slowed since, with 11 technicians said to have been killed in Germany since 2000.
But experts warn that the devices that remain could be getting more unstable as the munitions age and their fuses grow more brittle, and as bombs are discovered in more built-up, harder-to-reach areas.
The problem is also worse in certain parts of Germany. Oranienburg, just outside Berlin, has the dubious distinction of being the "most dangerous town in Germany". Under Adolf Hitler, it contained an armaments hub, aircraft plant, railway junction and a nuclear research facility - so it was a key target for the Allies, who gave it an aerial pounding. Almost 200 bombs have been defused in the town since the end of the war, and residents are well-drilled in the evacuation procedure. But with experts estimating that some 350-400 bombs remain buried, the task is far from complete.
Other WW2 bombs recently discovered in Germany
- May 2017: 50,000 people were evacuated from Hannover while three British-made bombs were defused
- December 2016: More than 50,000 evacuated in Augsburg over 1.8-tonne British explosive
- May 2015: 20,000 people in Cologne forced to leave their homes after a one-tonne bomb was discovered
- January 2012: A construction worker was killed when his digger hit an unexploded bomb in Euskirchen
- December 2011: 45,000 people were evacuated from Koblenz - half the total population - after two bombs were found in the riverbed of the Rhine
- June 2010: Three members of a bomb disposal squad were killed in Göttingen during an operation to defuse a bomb found on a building site