The number of migrants arriving on the Greek islands near Turkey has surged to about 7,000 a day in the past week, migration experts working there say.
The International Organization for Migration (IOM) said the average in late September was 4,500 a day.
Fears of worsening weather may account for the surge, the IOM says.
The EU's migrant relocation scheme got under way on Friday when 20 Eritreans left Italy on a flight to Sweden. Some EU member states object to the scheme.
Meanwhile, Turkey has voiced concern about the potential for even more Syrian migrants arriving at its border because of Russian air strikes in Syria.
The warning was issued by Turkish foreign ministry spokesman Tanju Bilgic. Turkey already hosts about two million Syrian refugees, many of whom are desperate to leave the emergency camps and start a new life in Europe.
Migrant arrivals in Greece 'surge' to 7,000 daily - IOM - BBC News