About 50,000 people in Hannover have been evacuated from their homes while experts defuse three British bombs dating from World War Two.
The operation is the second largest of its kind carried out in Germany, and has affected around a tenth of the city's population.
The buildings evacuated included seven care homes, a clinic and a Continental tyre plant.
Officials hope those affected will be able to return home by the evening.
The evacuation deadline was 09:00 (07:00 GMT) and residents were advised to take necessary items like medication with them, as well as turning off gas and electrical appliances.
Local news outlet Hannoversche Allgemeine reported [in German] on Sunday afternoon that two unexploded bombs had been defused, and a third - which was severely damaged - might have to be made safe using a specialised cutting machine.
Two other suspected bombs had turned out to be harmless scrap metal, it said.
No firm deadline has been given for when the restricted zone will return to normal. Road blocks have been set up to prevent cars from re-entering the area.
Emergency shelters have been established at three schools, and tens of thousands of soup portions prepared.
Bomb disposal experts had initially checked as many as 13 suspicious objects, but only five were found to merit further attention - two on a building site at the city's Wedelstaße, and three others nearby.
The city has set up a programme of museum tours, children's films and sporting events to help evacuees spend the day as pleasantly as possible.
Allied planes bombed Hannover heavily during World War Two, killing thousands and destroying much of the city.
On 9 October 1943, an especially deadly night, 1,245 people were killed and 250,000 left homeless by 261,000 bombs.
The largest bomb-related evacuation since the war happened on Christmas Day last year, in Augsburg.
Some 54,000 people had to be moved after a 1.8 tonne bomb was unearthed during building work.
Other WW2 bombs recently discovered in Germany
- 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 after two bombs were found in the riverbed of the Rhine. It took three hours to make them both safe.
- June 2010: Three members of a bomb disposal squad were killed in Goettingen during an operation to defuse a bomb found on a building site.