At least 11 people, seven of them children, drowned on Thursday after a boat carrying migrants from Turkey to Greece capsized near the island of Samos, the Greek coast guard said.
On Wednesday, seven migrants, including two children, drowned near the Greek island of Kos.
The Greek islands last year became the main gateway to Europe for people escaping war zones in the Middle East, but also for so-called economic migrants fleeing poverty in Asia and Africa.
The surge has continued in January, despite the danger of crossing the Aegean Sea in winter. UN refugee agency UNHCR has registered more than 44,000 arrivals since the start of this year.