An air and sea rescue operation was underway Wednesday after around 50 people went missing when a migrant boat sank in the Aegean Sea, the Greek coastguard said.

The vessel foundered at dawn off the islands of Karpathos and Rhodes after setting sail on Tuesday from Antalya, southern Turkey, heading for Italy.

"According to the statements of 29 rescued people, there were 80 people on the boat, so up to 50 people are missing," a coastguard press office official told AFP.

But state television channel ERT said the number of people on board had been between 30 and 60.

Coastguard spokesman Nikos Kokalas told the channel: "It's not possible that the boat could have been transferring 80 migrants. We are talking about a lower number."

The rescue effort, ordered by merchant shipping minister Yannis Plakiotakis, according to a coastguard statement, included four vessels already sailing in the southern Aegean, two coastguard patrol boats and a Greek air force helicopter.

Strong winds of up to 50 kilometres per hour (30 mph) were hampering the operation, Kokalas told Skai radio.

"Many of those shipwrecked were not wearing life-jackets," Kokalas said.

A video posted by the coastguard showed an army helicopter rescuing two survivors from the sea and transferring them to Karpathos.

Another 27 people were transferred to land aboard a tanker that joined the search off the island of Kos, said the coastguard.

- Dozens of deaths -
 

Although the migrant boat appears to have been trying to get to Italy, Greece is often the country of choice for people fleeing Africa and the Middle East to try to reach a better life in the European Union.

Thousands come to Greece via Turkey over the narrow and perilous sea crossing separating the traditional enemies.

Sixty-four people have perished in the eastern Mediterranean since January, the International Organization for Migration says.

Eight people died off the Greek island of Mykonos on June 19 when 108 more were rescued, according to the UN migration body.

The Greek coastguard on Sunday said 122 migrants were rescued near Rhodes after their vessel ran into trouble after sailing from Turkey.

Athens says migrant arrival numbers have climbed this year and accuses Ankara of not doing enough to stop smugglers from sending them across the border -- often in flimsy boats that make for dangerous journeys.

Turkey pledged under a 2016 deal to cut migrant numbers leaving its shores in return for financial aid from the European Union.

At the end of June, the EU urged Ankara to halt "violent and illegal expulsions" from its territory.

Charity groups and media accuse Athens of illegally turning back migrants, a charge Greece's conservative Greek government has denied.