It’s believed there were more than 500 people on the boat when it capsized (Picture: REUTERS)

The number of people confirmed dead after a migrant boat sank off the coast of Greece has reached 79.

It’s unclear how many people were aboard the boat but initial reports suggest hundreds of people were on board when it capsized.

The fishing boat sank on Wednesday, miles off the coast of Greece, and the coastguard, navy, merchant vessels and aircraft continued a search and rescue operation overnight.

An aerial photograph released by the Greek coastguard showed scores of people covering practically every inch of the ship’s deck – and it’s thought it capsized after people abruptly moved to one side.

Greece’s caretaker prime minister, Ioannis Sarmas, declared three days of national mourning, ‘with our thoughts on all the victims of the ruthless smugglers who exploit human unhappiness’.

Coastguard spokesman Nikos Alexiou told local TV: ‘The outer deck was full of people, and we presume that the interior (of the vessel) would also have been full.

‘It looks as if there was a shift among the people who were crammed on board, and it capsized.’

Rescue attempts were reportedly rebuffed by the boat’s passengers, who insisted they wanted to continue to Italy.

The Red Cross are supporting those rescued (Picture: Konstantinos Zilos/NurPhoto/Shutterstock)

25 people were hospitalised (Picture: AP Photos/Thanassis Stavrakis)

Those rescued were brought to shore in Kalamata (Picture: REUTERS)

Those rescued have been sheltering in a warehouse (Picture: REUTERS)

Ioannis Zafiropoulos, deputy mayor of the southern port city of Kalamata, where survivors were taken, said there could have been ‘more than 500 people’ on board.

The boat sank about 45 miles southwest of Greece’s southern Peloponnese peninsula, close to the deepest part of the Mediterranean Sea which could hamper efforts to locate the sunken vessel.

25 survivors have been hospitalised, while a further 70 were put up in a large warehouse in Kalamata with donated sleeping bags and blankets.

The coastguard said nobody on the ship had life jackets, and many of the people pulled from the water could not swim.

79 bodies have been recovered so far.

It’s believed the boat was sailing to Italy from the Tobruk area of eastern Lybia.

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‘The outer deck was full of people, and we presume that the interior (of the vessel) would also have been full.’