Hundreds of people were told to leave their homes and businesses in the English city of Bath on Thursday after a 500-pound (225-kilogramme) unexploded World War II bomb was found under a school playground.
Chief Superintendent Ian Smith, of Avon and Somerset police, told British broadcaster Sky News on Friday that military experts had brought 250 tonnes of sand to set up an exclusion zone around the unexploded bomb.
Police evacuated residents for 300 metres (328 yards) around the device, found during construction work at the disused Royal High School.
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Some spent the night at a local racecourse.
Smith told Sky News as many as 1,100 addresses, many of them commercial, had to be evacuated.
Bomb disposal experts plan to move the device outside the city where it can be exploded safely.
Police later said some residents might not be able to return until Saturday.
Britain was heavily bombed by Germany’s Luftwaffe during the war, and undetonated explosives are sometimes found during construction work.