Germany is willing to back Greece in dealing with the "extraordinary burden" of migrants landing on its shores every day, as the death toll from the latest boat sinkings rose to 15.
More than half a million people have arrived by sea in Greece this year seeking safety and a better life in Europe, and more than 3200 people have died making the perilous crossing from Turkey.
German Foreign Minister Frank-Walter Steinmeier, on a visit to Athens, said Berlin was ready to stand by Greece as it coped on the front line of Europe's biggest refugee crisis since World War II.
"At a moment when Greece is trying to recover economically, this influx is an extraordinary burden," Steinmeier told the Greek daily Ta Nea.
"We will support Greece as it faces up to this big challenge."
Europe, he said, "must demonstrate more courage in order to grow stronger".
"We must act together to take control of the situation, to safeguard Europe's external borders, to develop a common approach to asylum and immigration and to fairly share out the refugees," he said.
More than 700,000 people have reached Europe via the Mediterranean in 2015, according to the International Organisation for Migration (IOM), with many hoping to make it to Germany, the continent's economic powerhouse.
Most of those travelling to Greece have risked their lives making the dangerous sea crossing in overloaded, rickety boats.
Several sank off Greek islands in the Aegean Sea on Wednesday and on Thursday officials said the death toll had risen to 15, including 10 children, while about 40 people were still missing.
Two young children and two adults were found drowned on Thursday, a day after a boat carrying around 300 migrants overturned off the island of Lesbos. Rescuers managed to save some 240 people.
Elsewhere Spain's coastguard said it had rescued 15 migrants from a boat sinking off the coast of Morocco, but 39 others who were on board were missing.
The migrant crisis has opened up rifts between EU members over how to deal with the new arrivals.
Nations along the migrant trail northwards from Greece have been overwhelmed, and Hungary has sealed its southern borders with razor wire to stop the flow.