FRANKFURT, Germany (AP) — Thousands of people have been evacuated from a district of Frankfurt that includes the European Central Bank headquarters as authorities prepare to defuse a 500-kilo (1,100-pound) World War II bomb.

City officials called on some 16,500 people to leave their homes in the Ostend area Sunday morning, a few hours before the operation was scheduled to begin. Authorities already moved some people out of a nursing home on Saturday.

More than 70 years after the end of WWII, unexploded bombs are frequently found in Germany and disposing of them sometimes require large-scale precautionary evacuations. The American bomb in Frankfurt was found during construction work last month and officials chose Sunday to defuse it, giving them time to prepare the operation and minimizing disruption in Germany's financial capital.