About 20,000 residents in the western German city of Cologne are being forced to evacuate their homes after authorities discovered a 200kg WWII bomb.

Schools and kindergartens remained closed and dozens of ambulances were on the scene to evacuate residents of a nursing home.

The deactivation of the bomb, which was found near Muelheim bridge crossing the Rhine River, is planned for Wednesday afternoon.

City officials said in a statement that during this time the river would be closed for shipping and the air space would be closed too.

Even 70 years after the end of World War II, unexploded bombs are still found relatively frequently in Germany, generally during construction in major cities.

Cologne was a regular target for Allied bombers during the war.