Five migrants died early Saturday when a migrant boat sank off Crete, Greece's coastguard said, leaving 40 people reportedly missing while 39 survivors were rescued.

The boat sank 12 nautical miles southwest of the island, according to ERTNEWS, which reported the 40 missing.

A huge rescue operation involving vessels and aircraft was underway in the sea south of the island of Gavdos, south of Crete, after the boat capsized shortly after midnight, the coastguard said.

The first dead was found Saturday morning. 

Local media said another man was taken by helicopter to the hospital in the city of Chania on Crete and was admitted to intensive care.

Saturday afternoon, the coastguard told AFP that the number of migrants found dead had risen to five. 

Greece has seen a 25 percent increase this year in the number of migrants arriving, with a 30 percent increase to Rhodes and the southeast Aegean, according to the migration ministry.

Several similar accidents have occurred in recent weeks. In late November, eight migrants, six of them minors, died north of the island of Samos, on a route frequently used by people smugglers.