ATHENS, Greece (AP) — Greek authorities picked up 30 survivors from the sea Monday during a large rescue operation after a vessel carrying an unknown number of migrants sank off the southern island of Crete.

Efforts continued into the evening to locate other people who might be in the water. The coast guard said it was unclear whether anybody was missing, as the survivors were not in a position to give accurate numbers of how many had been on board when the vessel went down.

Initially, a person claiming to be a passenger who notified authorities by phone said 16 people were on the vessel that sank 12 miles (19 kilometers) east of Crete amid high winds Monday.

The coast guard said a Greek naval frigate and an air force helicopter were taking part in the search, together with two coast guard boats and three merchant ships.

There was no indication where the vessel sailed from, how big it was or where it had been heading to. Greece's east Aegean Sea islands are the typical destination of thousands of asylum-seekers from the Mideast, Africa and Asia who cross illegally from the nearby Turkish coast in hope of finding a better life in the European Union.

But on some occasions, smuggling gangs route yachts south of Crete to head for Italy.