The Greek coast guard defended its response to a ship that went down off the country’s south coast and left more than 500 migrants presumed drowned. Criticism mounted over Europe’s years-long failure to prevent such tragedies.

Patrol boats and a helicopter spent a third day scouring the area of the Mediterranean Sea where the packed fishing vessel capsized early Wednesday, in what the UN migration agency said could be the second deadliest migrant shipwreck recorded. The deadliest occurred when a vessel capsized off the coast of Libya en route to Italy in April 2015, killing an estimated 1100 people.

Greek coast guard spokesman Nikos Alexiou said that both coast guard and private ships repeatedly offered by radio and loudspeaker to help the vessel on Wednesday while it was in international waters, also heading from Libya to Italy, but they were rejected.

Alexiou argued that any effort to tow the overcrowded trawler or move hundreds of unwilling people onto nearby ships would have been too dangerous.

Scores of people covering practically every free stretch of deck on a battered fishing boat that later capsized and sank off southern Greece. Photo / Greece's Coast Guard

“Υou will have a disturbance, and the people will surge — which, unfortunately is what happened in the end,” Alexiou told state-run ERT TV. “You will have caused the accident.”

Alexiou also said that, after accepting food from a merchant ship, the trawler’s passengers rejected a rope bringing more from a second merchant ship “because they thought the whole process was a way for us to take them to Greece.”

Greek authorities sent the first ship, the tanker Lucky Sailor, to give the migrants food and water. The company managing the tanker said Friday that the people on board “were very hesitant to receive any assistance, and at any attempt of approach the boat started to manoeuvre away.”

Eastern Mediterranean Maritime Limited said in a statement that the people on the trawler were eventually persuaded to accept supplies.

Survivors of the latest tragic shipwreck prepare to board a bus to transfer to Athens at the port of Kalamata in Greece. Photo / AP

Experts said maritime law obligated Greek authorities to attempt a rescue.

They definitely “had a duty to start rescue procedures” given the condition of the vessel, said Professor Erik Røsæg of the University of Oslo’s Institute of Private Law. He said a refusal of assistance can be overruled if deemed unreasonable, as it appeared to have been on Wednesday.

Flavio Di Giacomo of the Mediterranean office of the UN migration agency IOM tweeted that all migrant boats should be considered dangerous and rescued immediately because “even when they appear to have no problems, in a few minutes they can sink.”

Rescuers pulled 104 survivors from the water and later recovered 78 bodies but have not located any more since late Wednesday. The Greek coast guard said the search-and-rescue operation would continue beyond the standard 72 hours.

The UN’s migration and refugee agencies issued a joint statement calling timely maritime search and rescues “a legal and humanitarian imperative” and calling for “urgent and decisive action to prevent further deaths at sea.”

A group of non-governmental organisations, including Amnesty International and Doctors Without Borders, said the EU should “stop seeing solutions solely in the dismantling” of smuggling networks, and set up state-led search-and-rescue operations in the Mediterranean.

“The Greek government had specific responsibilities toward every passenger on the vessel, which was clearly in distress,” Adriana Tidona of Amnesty International said. “This is a tragedy of unimaginable proportions, all the more so because it was entirely preventable.”

The round-the-clock effort continued off the coast of southern Greece despite little hope of finding survivors or bodies. Photo / AP

Greece and other southern EU nations that typically are the first destinations for Europe-bound asylum-seekers travelling by sea have toughened border protection measures in recent years, extending walls and intensifying maritime patrols.

“This is a European problem. I think it’s time for Europe to be able, in solidarity, to define an effective migration policy for these kinds of situations not to happen again,” UN Secretary-General Antonio Guterres said during a news conference at UN headquarters in New York late Thursday.

The EU’s executive commission says the 27-nation bloc is close to an agreement on how member countries can share responsibility in caring for migrants and refugees who undertake the dangerous journey across the Mediterranean.

A judicial investigation is also underway into the causes of the sinking. Greek officials say the vessel capsized minutes after it lost power, speculating that panic among the passengers may have caused the boat to list and roll over.

Most of the survivors were being moved Friday from a storage hangar at the southern port of Kalamata, where relatives also gathered to look for loved ones, to migrant shelters near Athens.

Abdo Sheikhi, a Kurdish Syrian living in Germany, travelled to Kalamata to find out what happened to five family members who were on the boat.

On Friday, he discovered that only his younger brother Ali and another relative had survived. He managed to speak on the phone to Ali, who has been moved to the camp near Athens.

“(Ali) told me he jumped (off the) ship while the others could not jump,” Sheikhi said. “They were scared. They were holding on to the boat as it swayed.”

Kassem Abo Zeed holds up a photograph with his wife, Ezra, who is missing after a fishing boat carrying migrants sank off southern Greece. Abo Zeed travelled from Hamburg, Germany, to try and find his wife and her missing brother, Abdullah Aoun. Photo / AP

Nine people — all men from Egypt, ranging in age from 20 to 40 — were arrested and detained and charged Friday of people smuggling and participating in a criminal enterprise. Twenty-seven of the survivors remain hospitalised, health officials said. The smuggling suspects are due to appear in court Monday.

The IOM has estimated the boat carried as many as 750 people, and UN human rights office spokesman Jeremy Laurence said the missing included “large numbers of women and children”.

The survivors were all boys and men from Egypt, Pakistan, Syria and the Palestinian territories. Alexiou, citing survivor accounts, said passengers in the hold of the fishing boat included women and children but that the number of missing, believed to be in the hundreds, still remained unclear.

Officials at a state-run morgue outside Athens photographed the faces of the victims and gathered DNA samples to start the identification process.

Late Friday, Greece’s coast guard said a navy helicopter located a sailboat with migrants off southwestern Greece after being alerted by Italian authorities. It said three merchant ships had reached the vessel, which reported no trouble and was heading for Italy. ERT TV said about 60 people were believed to be on board.

- Derek Gatopoulos, Nicholas Paphitis, AP