The death toll could climb however as rescuers are looking for dozens of people who are still missing, the coastguard said on Thursday morning.
Fifteen bodies were recovered near the eastern island of Lesbos after a dinghy carrying about 40 people sank. Five people were rescued and three had been located on a rocky outcrop near the site of the sinking.
Meanwhile, a second rescue effort was launched several hundred miles to the west, near the island of Kythira, where a boat carrying about 100 migrants sank late on Wednesday.
Officials said 30 people had been rescued after that vessel hit rocks off the village port of Diakofti on the east of the island. Winds in the area were up to 45mph.
Local resident Martha Stathaki said: “We could see the boat smashing against the rocks and people climbing up those rocks to try and save themselves. It was an unbelievable sight.
“All the residents here went down to the harbour to try and help.”
Fire service rescuers lowered ropes to help migrants climb up cliffs on the seafront.
Local officials said a school in the area would be opened to provide shelter for the rescued. Navy divers were also expected to arrive Thursday.
Most migrants reaching Greece travel from neighbouring Turkey, but smugglers have changed routes in recent months in an effort to avoid heavily patrolled waters around Greek islands near the Turkish coastline.
Greek migration minister Notis Mittarachi tweeted a call for Turkey to take “immediate action to prevent all irregular departures due to harsh weather conditions”.
“Already today many lives lost in the Aegean, people are drowning in unseaworthy vessels. EU must act,” he wrote.
Kythira is some 250 miles west of Turkey and on a route often used by smugglers to bypass Greece and head directly to Italy.