In the stadium of Monheim am Rhein, two bomb duds were discovered under the playing field.
The city announced on Wednesday that up to 2200 people would have to be evacuated within a radius of 400 meters from the site before the pending defusing.
Another 2400 people are said to be in closed rooms.
Monheim - The defusing was planned for noon.
Buses from several lines had to bypass the area.
The two explosive devices were discovered during ground probes before the planned renovation of the Jahn Stadium.
During the Second World War, Monheim near Düsseldorf was repeatedly the target of heavy air raids because of the mineral oil works located there.
The evaluation of aerial photographs taken after the air raids revealed two suspicious points.
Upon closer examination on site, the suspicion was confirmed.
dpa