Hopes for survivors dwindled on Thursday as rescuers scoured the seas off Greece following a shipwreck that killed at least 78 migrants, with fears growing 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 capsized and sank early on Wednesday morning in deep waters about 80 kilometers (50 miles) from the southern coastal town of Pylos. Greek authorities said 104 survivors had been brought ashore.

Outside the coast guard office in the port city of Kalamata, where survivors were transferred, a Syrian man whose wife was missing sought answers.

Kassam Abozeed, who lives in Germany, said he last heard from his wife Israa eight days ago. She had paid $4,500 to travel on the boat, the 34-year-old said, showing a photograph of her on his phone.

The search operation had not recovered any bodies in more than 24 hours, and victims' bodies were transferred to a cemetery near Athens for DNA tests. Government sources said chances of retrieving the sunken vessel were remote because of the depth of the water.

A shipping ministry official said nine Egyptians were arrested over the shipwreck. Greek TV Skai reported that, according to witnesses, the vessel departed from Egypt and stopped at the Libyan port of Tobruk before setting sail for Italy.

A European rescue-support charity said there could have been 750 people on the 20- to 30-meter-long (65- to 100-foot-long) boat. The U.N.'s International Organization 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.

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

'Our last night alive'

Independent refugee activist Nawal Soufi said in a Facebook post that she was in contact with migrants aboard the vessel from the early hours of Tuesday until 11 p.m.

"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.

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

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

But Greek officials said people on the crowded decks repeatedly turned down attempted assistance from a Greek coast guard boat shadowing it, saying they wanted to reach Italy.

"You cannot carry out a violent diversion on such a vessel with so many people on board... without any sort of cooperation," coast guard spokesperson Nikos Alexiou told state broadcaster ERT.

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

Government officials said that before capsizing and sinking around 2 a.m. on Wednesday, the vessel's engine stopped and it began veering from side to side.

'Watery graves'

On Thursday evening, thousands of leftist protesters rallied in Athens and the northern city of Thessaloniki demanding EU migration policies be relaxed. A group of protesters in Athens hurled petrol bombs at police who responded with tear gas.

In Kalamata, protesters marched outside the migrants' shelter. "Crocodile tears! No to the EU's pact on migration," read one banner.

EU migration policy "turns the Mediterranean, our seas, into watery graves," leftist Greek leader Alexis Tsipras, prime minister in 2015-2019 at the peak of Europe's migration crisis, said during a visit to Kalamata on Thursday.

Under a conservative government in power until last month, Greece took a harder stance on migration, building walled camps and boosting border controls.

The country is currently governed by a caretaker administration pending an election on June 25.

Greece's government spokesperson Ilias Siakantaris told Reuters that the biggest challenge for EU border states "is forging a comprehensive EU solution on migration and asylum that respects international law and inclusive humanism."

The United Nations has registered more than 20,000 deaths and disappearances in the central Mediterranean since 2014, making it the most dangerous migrant crossing in the world.