The German government accused Austria on Wednesday of driving refugees to the border after dark so they could cross into Germany and said it expected Vienna to return to an orderly processing of migrants immediately.

"The behaviour of Austria in recent days was out of order," Interior Minister Thomas de Maiziere told a news conference in Berlin, in the strongest public criticism of its neighbour since the refugee crisis deepened two months ago.

"We observed that refugees, without warning and after dark, were being driven to the German border without any provisions or forethought," he said.

"There were intensive contacts. Austria agreed yesterday to return to an orderly process. I expect this to occur immediately."