“The number of refusals will increase as a result of this measure alone,” she added.
Germany shares borders with nine countries: Poland, Austria, France, Denmark, the Czech Republic, Switzerland, Belgium, Luxembourg and the Netherlands. Ordinarily, travel between the countries, which are all part of the Schengen area, is seamless.
However, the new controls mean German police will carry out checks on people seeking to cross.
Germany faced a surge in irregular migration last year, with over 250,000 people suspected of entering the country illegally, according to the authorities.
With assistance from Tim Kummert and Jürgen Klöckner.