Rescue seemed so close at hand.

A ship with a crew experienced in plucking migrants from unseaworthy smuggler’s boats had arrived soon after the distress call went out from a fishing trawler packed with 850 people. But then the trawler’s navigator made a maneuver that would seal the fate of the those crammed inside: Instead of easing up alongside the merchant ship, he rammed into it.

Relief gave way to panic. Terrified migrants rushed to one side and the trawler capsized. What might have been another rescue in a period of unprecedented migrant crossings instead turned into a horrifying statistic: The deadliest shipwreck ever in the Mediterranean Sea.

The accounts of survivors who arrived early Tuesday in this Sicilian port 48 hours after the disaster offered new details of the tragedy. The traumatized witnesses corroborated a death toll of at least 800, making the capsizing “the deadliest incident in the Mediterranean that we have ever recorded,” the UN refugee agency said.

Just 28 migrants, all men and boys in their teens, survived. And despite the enormous toll, only 24 bodies were recovered — frequently the case when ships sink on the high seas, especially when most of their passengers are locked below deck, as was the case Saturday night.

Aid agencies were quick to issue another warning: At the current pace, 2015 is set to be the deadliest year on record for migrants making the perilous sea crossing as they flee war, repression and poverty in the Middle East and Africa. In April alone, 1,300 have died.

The International Organization for Migration said the toll for the year could top 30,000 — nearly 10 times the 2014 total of 3,279, itself a record.

“We just want to make sure people understand how much more … rapid these deaths have been coming this year,” said Joel Millman, the IOM spokesman.

Italian ships have rescued well over 10,000 people over the past two weeks, an unprecedented number for such a short period, authorities say. The rescues continued Tuesday, with another 112 migrants, all men, picked up in a deflating rubber life raft in waters some 50 miles north of the Libyan capital, Tripoli.

The weekend deaths have jolted the European Union onto emergency footing to combat the crisis, with Italy demanding that it not be left alone to shoulder the burden of rescues and that the EU focus on preventing boats from leaving Libya.

Combatting the traffickers by arresting ringleaders and destroying their boats has emerged as the centerpiece of a 10-point proposal to be discussed at an emergency EU summit Thursday in Brussels. Italy has arrested more than 1,000 smugglers — most of them boat navigators, not the masterminds of the smuggling operations — and says it needs help.

Among the survivors of Saturday’s sinking were two alleged smugglers, who were detained for investigation of aiding and abetting illegal immigration. The Tunisian navigator, identified as 27-year-old Mohammed Alì Malek, could also face multiple counts of manslaughter and causing a shipwreck.