German Chancellor Angela Merkel was facing fresh pressure on Monday after a regional election drubbing described as a "debacle" over her liberal refugee policy.

Merkel's Christian Democratic Union was at the receiving end of voters' anger, suffering defeats in two out of three states in regional elections - including its traditional stronghold Baden-Wuerttemberg.

The stinging result for the conservative CDU was accompanied by a surge in backing for the right-wing populist Alternative for Germany, or AfD, which had sparked outrage by suggesting police may have to shoot at migrants to stop them entering the country.