Greek authorities say 21 people have died after two boats carrying migrants and refugees from Turkey to Greece sank overnight, in the latest deadly incidents in the eastern Aegean Sea.

The Merchant Marine Ministry said 18 people were killed and 138 people were rescued near the island of Kalymnos, while another three died and six were rescued in a separate incident early Friday off the island of Rhodes.

The deaths occurred amid a surge of crossings to Greek islands involving migrants and refugees from Syria, Afghanistan and other countries ahead of winter and as European governments weight taking tougher measures to try and limit the number of arrivals in Europe.

Eight people were killed early Thursday after a boat capsized off the island of Lesbos.