Rescue vessels fanned out on Thursday in search of hundreds of refugees and migrants feared dead after their overcrowded fishing boat capsized and sank as they tried to reach Europe.
At least 79 people died in the disaster.
Rescue workers rescued 104 passengers from the boat that sank in deep waters off the Greek coast early Wednesday morning while trying to travel from Libya to Italy.
Authorities fear that hundreds of others – including women and children – could be trapped below decks.
If confirmed, it would make the tragedy one of the worst ever recorded in the Central Mediterranean.
“The chance to find [more survivors] are minimal,” retired Admiral Nikos Spanos of the Hellenic Coast Guard told state television ERT.
The International Organization for Migration estimated, based on interviews with survivors, that the ship was carrying 700 to 750 people, including at least 40 children. Save the Children raised that number to about 100 children.
Reports suggested the boat sank about 80 km (50 mi) from the southern coastal town of Pylos.
Refugee activists, refugee rescue NGOs, some European politicians and Pope Francis were among those who shared their grief and anger at the disaster.
The Vatican said the pope was “deeply stunned” and expressed “heartfelt prayers for the many migrants who died, their loved ones and all those traumatized by this tragedy”.
‘Should be a wake-up call for EU governments’
Aerial photos released by the Greek Coast Guard showed dozens of people on the boat’s upper and lower decks looking up, some with their arms outstretched, hours before it sank.
Alarm Phone, which operates a trans-European network that supports rescue operations, said it received alerts from people aboard a ship in distress off the coast of Greece late Tuesday night.
It said it alerted Greek authorities and spoke to people on the ship calling for help, and that the captain had fled on a small boat.
Government officials said before capsizing and sinking around 2 a.m. Wednesday, the ship’s engine stopped and it began to rock back and forth.
Most of the survivors transferred to the port city of Kalamata so far have been men, authorities said.
Al Jazeera’s John Psaropoulos, reporting from Kalamata, said doctors treated several survivors, dozens of whom showed symptoms of “near drowning.”
“They suffered from a type of pneumonia that occurs when the lungs are partially flooded with water,” he said. “Some have been sent back to a warehouse where other survivors were staying.”
When Greece declared three days of mourning, the bodies of the victims were transferred to a cemetery near Athens for DNA testing. The search will continue for as long as necessary, the Coast Guard said.
“[European Union] Member States have gone to extraordinary lengths to close all routes to children and their families seeking safety in Europe. Often their only option is to make dangerous journeys by boat,” said Daniel Gorevan, senior advocacy advisor at Save the Children.
“The fact that people are still dying in the Mediterranean should be a wake-up call for EU governments,” he warned.
Government sources said there was little chance of recovering the sunken ship that had departed from the Libyan port of Tobruk. The area of international waters where the incident took place is one of the deepest in the Mediterranean.
Independent refugee activist Nawal Soufi said in a Facebook post that she had been approached by people aboard the ship in the early hours of Tuesday and had been in contact with them until 11pm (20:00 GMT).
“All the time they asked me what to do and I kept saying that Greek help would come. On this last call, the man I spoke to said emphatically, ‘I feel like this will be our last night alive,'” she wrote.
Greece is one of the main routes to the EU for refugees and migrants from the Middle East, Asia and Africa.
Under a conservative government in power until last month, Greece has taken a tougher stance on migration, building walled camps and stepping up border controls.
The country is currently run by a caretaker government pending elections on June 25.
Libya, which has seen little stability or security since a NATO-backed uprising in 2011, is an important starting point for those seeking to reach Europe by sea, as its human-smuggling networks are mainly led by military factions that control coastal areas.
The United Nations has recorded more than 20,000 deaths and disappearances in the central Mediterranean since 2014, making it the most dangerous migrant crossing in the world.