A government spokeswoman said Chancellor Angela Merkel will interrupt a summer holiday to attend the memorial.
The memorial will be held in the city of Duisburg, the city in Germany's western industrial region where the disaster occurred on Saturday. More than 500 people were also injured.
Duisburg's city hall said it would be held in one of the city's churches.
The 20 victims were crushed or trampled to death last Saturday at the festival when panic broke out in a tunnel filled with people.
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