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

The boat, which was carrying around 50 people, took on water near the island of Paxi during an apparent attempt to reach Italy.

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

Six coastguard patrol boats and three helicopters were engaged in the continuing rescue effort, authorities said.

Four passing cargo ships are also assisting the operation.

Thousands of migrants and refugees have died in recent years while attempting to cross the Mediterranean Sea in small, overloaded boats.

With Greece's northern borders closed to migrants seeking to reach western Europe, some are trying clandestine routes to quit the country, such as mountain routes into Albania or by sailing to neighbouring Italy.

Twenty-two people have died or are still missing in migrant boat sinkings in the Mediterranean just this month, according to the International Organization for Migration.

Another 73 people were rescued in separate incidents in the Aegean between Friday and Saturday, the Greek coastguard added.

Greece in 2019 again became the main entry into Europe for migrants and refugees. The UN refugee agency recorded more than 55,000 arrivals by sea, and more than 14,000 via the land border with Turkey.