A fishing boat with up to 500 migrants on board was rescued in stormy seas south-west of Crete on Tuesday.
The coastguard received a distress call shortly before midnight.
“The call said there are 400-500 people on board,” a spokeswoman said, adding the rescue operation had been hampered by near gale-force winds.
“They can see the boat, it's adrift, there is a large number of people on board,” she added.
Two nearby cargo ships, a tanker and two Italian fishing boats, were lending assistance.
Because of bolstered patrols by the Greece and EU border agency Frontex in the Aegean Sea, migrant-smugglers are increasingly employing the longer and more perilous route south of Crete, Greek officials say.
“Eighty per cent of flows from Turkey go straight to Italy,” Migration Minister Notis Mitarachi told Skai TV last week.
Last month, a sailboat believed to have 95 people on board sank off the island of Kythira, south of the Peloponnese peninsula.
The boat went down beneath a huge vertical cliff. At least eight people died and survivors, who were mainly from Iraq, Iran and Afghanistan, were hauled to safety with ropes and a construction crane in a frantic predawn operation.
Greece, Italy and Spain are among the countries used by people fleeing Africa and the Middle East in search of safety and better lives in the EU.
The Greek coastguard has said it has rescued about 1,500 people in the first eight months of the year, compared with less than 600 last year.
Migrants cross from Morocco to Spanish enclave of Melilla — in pictures
The International Organisation for Migration has recorded nearly 2,000 migrants killed and missing in the Mediterranean Sea this year.
EU interior ministers will meet this week to discuss the migrant crisis, officials announced on Thursday, after a row erupted between France and Italy over the arrival of migrants rescued at sea.
An extraordinary meeting of the Home Affairs council will take place on November 25 in an attempt to resolve the dispute, diplomats in Brussels said.
“Ministers will address the current situation in all migratory routes,” the EU's Czech presidency said.