At least 12 people died Saturday when a boat loaded with asylum-seekers sank in the Ionian Sea, the Greek coastguard said.

"So far 12 bodies have been recovered. The search and rescue operation continues," they said in a statement, adding that they had rescued more than 20 survivors.

"Three of them are being flown by helicopter to (the nearest hospital) for emergency treatment," the statement added. There were no immediate details on the identity of those on board.

The boat, which was carrying around 50 people, took on water near the island of Paxi during an apparent attempt to reach Italy. At this point someone on board issued a distress call, the authorities said.