June 4 (UPI) -- More than 20,000 people in Germany were evacuated as authorities worked Wednesday to defuse three huge unexploded bombs from World War II at a construction site in the center of the city.

A major incident was declared due to the danger from the bombs -- two 2,200 lb devices and one of 1,100 lbs -- with police making checks door-to-door in the Old Town and Deutz areas of Cologne after 20,500 people were ordered to leave and businesses, tourist attractions and stations were shuttered, the city said in a news release.

The 1,100-yard-wide exclusion zone covers the city's UNESCO-listed 13th-century cathedral, 58 hotels, parts of the subway system, at least nine schools, day care centers, two retirement homes, a hospital, as well as city hall and many other sites.

"The evacuation is the largest measure since the end of the Second World War. Everyone involved hopes that the defusing can be completed in the course of Wednesday," city authorities said.

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