ROME, Italy (AFP) – Up to 700 people were feared drowned Sunday after an overcrowded boat smuggling them to Europe capsized off Libya in the latest and deadliest in a long list of migrant disasters in the Mediterranean.

Italy’s coastguard, which was coordinating the search for survivors and bodies, said only 28 people had survived a wreck that triggered fresh calls from Pope Francis and others for European leaders to act over what many saw as an avoidable tragedy.

Survivors’ testimonies suggested there had been about 700 people on board the 20-metre (70-foot) fishing boat when it keeled over in darkness overnight, officials said.

“It seems we are looking at the worst massacre ever seen in the Mediterranean,” UNHCR spokeswoman Carlotta Sami said.

As Italy demanded an emergency summit of European Union leaders, talks at the level of foreign ministers were scheduled for Monday to discuss what Amnesty International blasted as a predictable “man-made tragedy”.

Coastal authorities in Italy and Malta picked up a distress signal from the stricken vessel around midnight (on Saturday, when it was about 70 miles (126 km) off the Libyan coast.

The Italian coastguard instructed a nearby merchant ship to provide assistance and it was when the Portuguese-registered King Jacob arrived at the scene that the fishing boat capsized, most likely as a result of the terrified passengers stampeding to one side in their desperation to get off, the UNHCR’s Sami said.

Italian, Maltese and merchant boats scoured the area for survivors on Sunday but only 24 bodies were recovered. They were being taken to Malta.

Italian Prime Minister Matteo Renzi said the coastguard would seek to salvage the boat and ensure any corpses recovered from it were given a decent funeral.

EU foreign policy chief Federica Mogherini, a former Italian foreign minister, said Sunday’s events were a stain on the EU’s conscience.

“We have said too many times ‘never again’. Now is time for the European Union as such to tackle these tragedies without delay.”

The UN High Commissioner for Refugees, Antonio Guterres, added: “This disaster confirms how urgent it is to restore a robust rescue-at-sea operation and establish credible legal avenues to reach Europe. Otherwise people seeking safety will continue to perish at sea.”

The disaster was the latest in a growing catalogue of mass drownings of migrants attempting to reach Europe on overcrowded, unseaworthy boats run by people smugglers who are able to operate out of Libya with impunity because of the chaos engulfing the north African state.

The most serious incident prior to Sunday occurred off Malta in September 2014. An estimated 500 migrants drowned in a shipwreck caused by traffickers deliberately ramming the boat in an attempt to force the people on board onto another, smaller vessel.

In October 2013, more than 360 Africans perished when the tiny fishing boat they were crammed onto caught fire within sight of the coast of Lampedusa.

That horrific tragedy was described at the time as a wake-up call to the world but 18 months later there is no sign of a let-up in the numbers attempting the perilous crossing in search of a better life in Europe.

The latest disaster comes after a week in which two other migrant shipwrecks left an estimated 450 people dead.

If the worst fears about Sunday’s tragedy are confirmed, it will take the death toll since the start of 2015 to more than 1,600.

More than 11,000 other would-be immigrants have been rescued since the middle of last week and current trends suggest last year’s total of 170,000 migrants landing in Italy is likely to be exceeded in 2015.

Pope Francis said European Union leaders must act.

“These are men and women like us, brothers seeking a better life,” he said in his weekly address to the Roman Catholic faithful in St Peter’s square, urging leaders to “act decisively and quickly to stop these tragedies from recurring.”

Amnesty’s John Dalhuisen called Sunday’s accident a “man-made tragedy of appalling proportions.”

“These latest deaths at sea come as a shock, but not a surprise.”

Amnesty is among NGOs calling for the restoration of an Italian navy search-and-rescue operation known as Mare Nostrum which was suspended at the end of last year.

Italy scaled back the mission after failing to persuade its European partners to help meet its operating costs of nine million euros ($9.7 million) a month amid divisions over whether the mission was unintentionally encouraging migrants to attempt the crossing.

Mare Nostrum has been replaced by a much smaller EU-run operation called Triton which has only a fraction of the specialist assets and manpower.