German Chancellor Angela Merkel is coming under severe pressure over her 'open door' policy on refugees and migrants as her Interior Minister Thomas de Maiziere joined calls for a cap on the number coming into the country.

Merkel has been criticized in Germany and outside for encouraging the mass migration which has led to millions moving within Europe and the closure of borders, challenging one of the fundamental principles of the European Union — the freedom of movement.

Merkel's personal popularity has plummeted since the start of the crisis and there have been frequent demonstrations on the streets — most recently in Dresden where around 9,000 members of the anti-migrant movement PEGIDA to rally against the country's plans to take in people fleeing war and poverty in the Middle East and Africa.

One banner at the rally read: "Merkel is guilty" accusing her of "ethnocide against the German people."

There have also been arson attacks on asylum shelters across Germany as it struggled to deal with the massive influx of migrants and refugees. De Maiziere said:

"That's why we have to limit the numbers and find the right balance. Our capabilities are limited."

Calls for Border Closures

Merkel's Bavarian allies have accused her of unwittingly encouraging more refugees to come to Germany by stating publicly there was no upper limit to the number that would be accepted.

Conservative politicians have urged Merkel to come out in favor of a maximum number. In addition, Finance Minister Wolfgang Schaeuble has said Europe needs to restrict the number of people coming to the continent.

Members of the Christian Social Union (CSU), the sister party to Merkel's conservatives in Bavaria, said Germany should shut its borders. Bavaria shares a border with Austria and has borne the brunt of the influx.

"If as many asylum seekers continue to come to Germany as in recent weeks, we won't have any choice but to temporarily stop taking people in and to close the borders to them," CSU politician Stephan Mayer told the newspaper Frankfurter Allgemeine Zeitung.

But Merkel so far has rejected to give way, saying in a radio interview aired on Sunday that Germany must tackle the crisis head-on rather than trying to get rid of the problem.

German authorities meanwhile, expect up to 1.5 million refugees to come to the country this year, up from a previous estimate of 800,000 to 1 million, according to a document seen by the Bild newspaper.

However, government spokesman Georg Streiter denied all knowledge of the document, saying: "No-one knows this paper. For that reason I wouldn't put too much credence in it."