At least four people died and desperate efforts were underway Friday to find hundreds more believed missing after a migrant boat capsized off the Greek island of Crete, the coastguard said.

Coastguard spokesman Nikos Lagadianos said at least 340 people had been rescued, and the International Organization for Migration (IOM) said the vessel "is believed to have left Africa with at least 700 migrants on board".

It was the second migrant vessel found in that area of the southern Aegean Sea since last week, indicating that people smugglers may be forging a new route to avoid NATO ships, the Daily Mail reported. 

A coastguard spokeswoman said a major rescue operation was underway, including four ships that were passing through the area, in clear but windy conditions about 75 nautical miles south of Crete.

"The number of people in distress could be counted in the hundreds," she said.

It was not immediately clear where exactly the boat had left from or where it was headed, or the nationalities of those on board.

The coastguard spokeswoman said a passing ship spotted the sinking vessel off Crete.

The coastguard rushed two patrol boats, a plane and a helicopter to the scene.

About half of the 25-metre-long boat was completely underwater, the spokeswoman said. 

Source ; MENA