Rescuers have scoured the seas off Greece following a shipwreck that killed at least 78 migrants, as hopes of survivors dwindled and fears grew that hundreds more, including children, may have drowned inside the crowded vessel’s hold.

Reports suggested between 400 and 750 people had packed the fishing boat that departed the Libyan port of Tobruk and capsized and sank early on Wednesday morning in deep waters about 80km from the southern coastal town of Pylos.

Greek authorities said 104 survivors had been brought ashore.

Even before it began to flounder late on Tuesday night, people on the vessel’s crowded outer deck repeatedly turned down attempted assistance from a Greek coast guard boat that was shadowing it, saying they wanted to reach Italy, according to Greek authorities.

“When you are faced with such a situation… you need to be very careful in your actions,” coast guard spokesman Nikos Alexiou told state broadcaster ERT.

“You cannot carry out a violent diversion on such a vessel with so many people on board… without any sort of co-operation.”

As Greece declared three days of mourning, authorities said it was unclear how many had been aboard.

They were investigating an account from a European rescue-support charity that there could have been 750 people on the 20- to 30-metre-long boat.

The United Nations’ International Organisation for Migration said initial reports suggested up to 400 people were aboard.

Its refugee agency, the UNHCR, said hundreds were feared missing.

“The shipwreck off Pylos marks one of the largest sea tragedies in the Mediterranean in recent memory,” Maria Clara, the UNHCR representative in Greece, told Reuters, adding the UNHCR urged Mediterranean countries to establish a fast and predictable search and rescue regime and increase safe routes.

Pope Francis, who visited Greece two years ago to draw attention to the plight of migrants and refugees was “deeply dismayed to learn of the shipwreck… with its devastating loss of life,” the Vatican said in a statement.

Of the 104 survivors so far transferred by the coast guard to the Greek port city of Kalamata, most were men, authorities said.

They revised their overnight death toll to 78 from 79.

On Thursday, bodies of the victims were transferred to a cemetery near Athens for DNA tests.

The search operation had not recovered any bodies in the past 24 hours and the coast guard said it would continue for as long as needed.

But government sources said chances of retrieving the sunken vessel were remote because of the depth of the water.

Aerial pictures released by the Greek coast guard showed dozens of people on the boat’s upper and lower decks looking up, some with arms outstretched, hours before it sank.

Alarm Phone, which operates a trans-European network supporting rescue operations, said it received alerts from people on board a ship in distress off Greece late on Tuesday.

It said it had alerted Greek authorities and spoke to people on the vessel who appealed for help, and that the captain had fled on a small boat.

Government officials said that before capsizing and sinking about 2am on Wednesday, the vessel’s engine stopped and it began veering from side to side.

Independent refugee activist Nawal Soufi said in a Facebook post that she was contacted by migrants aboard the vessel in the early hours of Tuesday, and that she had been in contact with them until 11pm.

“The whole time they asked me what they should do and I kept telling them that Greek help would come. In this last call, the man I was talking to expressly told me: ‘I feel that this will be our last night alive’,” she wrote.

On Thursday, a senior prosecutor took over the supervision of the investigation launched by coast guard authorities over the incident, state broadcaster ERT reported.

Greece is one of the main routes into the European Union for refugees and migrants from the Middle East, Asia and Africa.

Source: AAP