ATHENS, Greece (AP) — A large-scale rescue operation was underway off a southern Greek island where a sailboat carrying up to 100 migrants hit rocks and sank in high winds late Wednesday, authorities said.

The coast guard said its vessels, private boats and a rescue helicopter were involved in the effort off the coast of the island of Kythira, some 225 kilometres (140 miles) south of Athens.

Officials said seven people had been rescued so far but gave no other details on the missing. They said the sailboat hit rocks off the village port of of Diakofti on the east of the island. Winds in the area were up to 70 kph (45 mph).

“We could see the boat smashing against the rocks and people climbing up those rocks to try and save themselves. It was an unbelievable sight,” Martha Stathaki, a local resident told The Associated Press. “All the residents here went down to the harbor to try and help.”

Fire service rescuers lowered ropes to help migrants climb up cliffs on the seafront. Local officials said a school in the area would be opened to provide shelter for the rescued.

Most migrants reaching Greece travel from neighboring Turkey, but smugglers have changed routes in recent months in an effort to avoid heavily patrolled waters around Greek islands near the Turkish coastline.

Kythira is some 400 kilometres (250 miles) west of Turkey and on a route often used by smugglers to bypass Greece and head directly to Italy.