German police said Saturday the stabbing of a prominent candidate for Sunday's mayoral election in Cologne had a "racist political" motive linked to the huge numbers of migrants entering the country.

Henriette Reker, who suffered serious stab wounds to the neck during the morning assault, was "responsible for taking charge of refugees" in the city, regional police head Wolfgang Albers said in a statement, suggesting it was a "political act".

Another police official also suggested the attack had a "racist motivation".