The number of people seeking asylum in Germany this year will be as high as 1.5 million – almost double the previous estimate, German media report.
The German government has not confirmed the new estimate, which comes from an internal official report cited by popular daily Bild.
The report warns that services helping refugees will not be able to cope.
Separately, a centre-right regional minister put the expected total at 1.2-1.5 million for this year.
The German government previously estimated the number of asylum claims this year to reach 800,000 to one million in total.
Many are refugees fleeing the wars in Syria, Iraq and Afghanistan, but there are also many economic migrants from the Balkans, Asia and Africa.
UN High Commissioner for Refugees Antonio Guterres has warned that Europe, in dealing with the migration crisis, is engaged in a “battle of compassion versus fear, and of tolerance versus xenophobia”.
Speaking in Geneva, he said the world was facing the highest levels of forced displacement in recorded history and the principle of asylum must remain sacrosanct.
He urged Europe to defend “its founding values of tolerance and openness by welcoming refugees of all religions”.
The leaders of Hungary and Slovakia have said the influx of Muslims is a challenge to Europe’s “Christian” identity.
The Turkish President, Recep Tayyip Erdogan, is to meet EU leaders in Brussels shortly to discuss the Syria crisis, which has fuelled an exodus of Syrians to the EU via Turkey.
Greek islands near the Turkish coast are overburdened with migrants, many of them Syrians determined to reach Germany. The crisis has strained EU relations with Turkey, a mainly Muslim country.