Greece's coast guard said it rescued 542 people in 12 search and rescue incidents from Thursday morning to Friday morning.
The rescues occurred off the coasts of the eastern Aegean islands of Lesbos, Chios, Samos, Agathonissi and Farmakonissi, the coast guard said.
Hundreds of thousands of people fleeing war and poverty in their homelands have reached Greece so far this year, the vast majority on rickety boats or cheap inflatable dinghies from the nearby Turkish coast. Although a short sea journey, it can be fatal as the unseaworthy and overloaded boats sometimes sink.
Very few of those arriving in Greece want to stay in the financially stricken country, instead moving north through the Balkans to more prosperous European Union countries such as Germany, Austria and Sweden.