A fishing boat carrying migrants trying to reach Europe capsized and sank Wednesday off the coast of Greece, authorities said, leaving at least 79 dead and many more missing in one of the worst disasters of its kind this year.

The Greek government declared three days of national mourning “for the victims of today’s tragic shipwreck in international waters west of Greece, with the thought and to all victims of unscrupulous traffickers who exploit human misery.”

Because the incident took place in international waters, it is not just a Greek tragedy but a European one, too. The European Council president, Charles Michel, said on social media that he was “deeply saddened” by the calamity and that the EU’s immediate response would be to “address the issue” of people smuggling at an upcoming meeting. 

That rather undramatic response to the latest catastrophe in the Mediterranean is all the more surprising because just this month EU leaders hailed a new voluntary solidarity mechanism for various countries, including France and Germany, to take in refugees. The measure is aimed at handling migrants rescued at sea — but does nothing to prevent migrants from attempting to get to Europe. 

Not all EU countries were in favor of the initiative, with some such as Austria maintaining that it sends the wrong message to human traffickers. 

The European Commission president, Ursula von der Leyen, tweeted that she was “deeply saddened by the news of the shipwreck … and the many reported deaths.”

Tweeting is the easy part. On Wednesday, Greek coast guard, navy, and merchant vessels and aircraft fanned out for a vast and complex search-and-rescue operation set to continue overnight. It was unclear how many passengers were still missing.

A coast guard spokesman, Nikos Alexiou, told state ERT TV: “The outer deck was full of people, and we presume that the interior would also have been full,” he said. “It looks as if there was a shift among the people who were crammed on board and it capsized.”

The deputy mayor of the southern port city of Kalamata, where survivors were taken, Ioannis Zafiropoulos, said that his information indicated there were “more than 500 people” on board.

“It sank very quickly and was gone by the time the rescue helicopter got there,” he said. “The area where this happened has very deep water.”

Authorities said 104 people were rescued after the boat sank in international waters about 45 miles southwest of Greece’s southern Peloponnese peninsula. The spot is close to the deepest area of the Mediterranean Sea, and the depth could hamper any effort to locate a sunken vessel.

Rescuers said many of the people pulled from the water couldn’t swim and were clutching debris. The coast guard said none had life jackets.

The Greek coast guard said that 79 bodies have been recovered so far. Survivors included 30 people from Egypt, 10 from Pakistan, 35 from Syria, and two Palestinians, the agency said.

The Italy-bound boat was believed to have left the Tobruk area in eastern Libya — a country that descended into chaos following a NATO-backed uprising that toppled and killed the longtime autocrat leader, Moammar Gadhafi, in 2011. Human traffickers have benefited from the instability, and made Libya one of the main departure points for people attempting to reach Europe on smuggler’s boats.

The route to Italy from North Africa through the central Mediterranean is the deadliest in the world, according to the UN migration agency, known as IOM, which has recorded more than 17,000 deaths and disappearances there since 2014.

Smugglers use unseaworthy boats and cram as many migrants as possible inside — sometimes in locked holds — for journeys that can take days. They head for Italy, which is directly across the Mediterranean from Libya and Tunisia, and much closer than Greece to the Western European countries that most migrants hope to eventually reach.

In February, at least 94 people died when a wooden boat from Turkey sank off Cutro, in southern Italy, in the worst Mediterranean sinking so far this year.

The Italian coast guard first alerted Greek authorities and the European Union border protection agency, Frontex, about an approaching vessel on Tuesday.

The Mediterranean’s deadliest shipwreck in living memory occurred on April 18, 2015, when an overcrowded fishing boat collided off Libya with a freighter trying to come to its rescue. Only 28 people survived. Forensic experts concluded that there were originally 1,100 people on board.

The Greek president, Katerina Sakellaropoulou, visited the area where rescued migrants are being tended to, and political parties called off planned campaign events before a June 25 national election.

A former prime minister, Kyriakos Mitsotakis, who is widely expected to win re-election, said the emergency “dramatically highlights how migration is a problem that requires a cohesive European policy, so that the vile criminal networks that smuggle desperate people at last meet with the decisive response that they deserve.”

As the latest maritime disaster shows, such a cohesive policy, while badly needed, is proving stubbornly elusive.