Some 70,000 people in Frankfurt will have to leave their homes this weekend in one of the biggest such evacuations in post-war Germany, police said Wednesday, after an unexploded World War-II bomb nicknamed "blockbuster" was uncovered.

The operation on Sunday will allow for the safe defusal of the 1,400-tonne British bomb, which German media said was nicknamed "Wohnblockknacker" (blockbuster) during the war for its ability to wipe out whole streets or buildings.

Dating back to the Allies' raids on the city, the 1.8-ton HC-4000 type British bomb was discovered during construction work in the upmarket Westend district.

Officers are guarding the site and there "is currently no danger".

"Due to the large size of the bomb, extensive evacuation measures must be taken," police said.

The Wismarer street where the ordnance was found is close to the city center and just some 2.5 kilometers (1.5 miles) north of the main Zeil shopping area.

German authorities said it remained unclear what repercussions the action to defuse the bomb would have on air traffic over Frankfurt, which is the nation's biggest airport.

This could depend on the wind conditions prevailing on Sunday when the moves to defuse the bomb are under way, they said.

More than 70 years after the end of the war, unexploded bombs are regularly found buried on German land, legacies of the intense bombing campaigns by the Allied forces against Nazi Germany.

About 54,000 people were forced to leave their homes in the Bavarian city of Augsburg at the end of last year, while in May of this year, 50,000 residents were evacuated from the central city of Hanover in order to defuse a wartime bomb there.