At first I thought they were afraid it was a nuclear bomb, to evacuate so many poeple.

I forgot that in Japan 16,000 poeple live easily in a 500 meters radius.
Tokyo ordered about 16,000 residents to evacuate on Sunday while a bomb squad disposed of an unexploded bomb believed to have fallen during World War II in western Tokyo, Kyodo News said.
Ground Self-Defense Force members removed the fuse of the dud in a two-hour operation earlier in the day, and the Chofu city government declared the area safe and called off the alert, Kyodo said.
The local government ordered people living in a radius of about 500 meters around the scene to evacuate and suspended part of train services in the area, it said.
The 180-centimeter-long, 600-centimeter-diameter dud, believed to be a 1-ton bomb which was apparently dropped from a U.S. B-29 bomber which crashed in April 1945, was found in March this year, Kyodo said.
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