Chancellor Angela Merkel vowed Wednesday on a visit to a refugee centre that Germany would have "no tolerance" for "shameful and vile" attacks on asylum-seekers, after a wave of violent protests.

"There will be no tolerance of those who question the dignity of other people," she said in the small eastern town of Heidenau which saw far-right riots against police guarding a new refugee shelter.

"The more people who make that clear... through their work and also in conversations with acquaintances, friends and families, the stronger we will be and the better we will be able to address this task" of caring for refugees.