Update 1:20 p.m. ET

BERLINGerman authorities safely defused a huge bomb left over from World War II after evacuating large parts of the western city of Dortmund on Sunday.

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More than 20,000 people were evacuated from their homes in Dortmund as authorities prepared to take action following the bomb's discovery.

The 4,000-pound bomb was uncovered after experts analyzed old aerial photographs while searching for unexploded ordnance dropped by Allied aircraft over Germany's industrial Ruhr region.

While unexploded WWII-era bombs are regularly discovered in Germany, they are rarely as big as this one.

A similar bomb find two years ago prompted the evacuation of some 45,000 people in the city of Koblenz along the Rhine river.