Rescue seemed so close at hand.

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

Relief gave way to panic. Terrified migrants rushed to one side, the trawler seized and 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 U.N. 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 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 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.

On Tuesday, seamen who participated in saving survivors of the weekend capsizing told tales of near-miraculous rescue.

Among the ships to arrive in the pre-dawn hours Sunday was the coast guard ship Gregoretti, which dispatched medics in two dinghies. By then, the trawler had already disappeared into the sea.

"We found, literally, a floating cemetery. Bodies were everywhere. With the dinghies we had to literally slalom among the corpses," said Enrico Vitello, a 22-year-old medic from the Order of Malta.

Hearing screams, they killed the engines and shined a spotlight, locating a migrant floating in the sea.

"We got close by and rescued him," said Giuseppe Pomilla, a 30-year-old medic. "He asked our names and where we were from. We told him we were Italians and came to rescue him. He was so happy."

Soon after, a boy floating in the sea grabbed their attention.

"We couldn't understand if he was alive or dead. He had his eyes wide open looking at us. He was not blinking, not moving or talking. We only realized he was alive when he grabbed us suddenly," Pomilla said.

When they took him on board, he "exploded in tears," the medic said.

Among the survivors 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 — the same charges the captain of the capsized Concordia luxury cruise liner was convicted of earlier this year.

Prosecutors said that after the trawler's captain struck the Portuguese-flagged container ship sent to rescue it, terrified migrants rushed to one side of the overcrowded boat, which was already unbalanced from the collision. The trawler pitched in the water before finally tipping over and sinking.

Most on board were unable to escape because they were locked below deck on the trawler's lower two levels. Hundreds more were squeezed on the upper deck.

"The survivors said that the person who was steering the boat, their smuggler, was navigating badly, and he did a bad move that made it crash against the bigger ship," UNHCR spokeswoman Carlotta Sami said in Sicily. "This obviously created a problem because the people on the lower decks couldn't get out and the boat destabilized, until it capsized."

She praised the merchant ship, the King Jacob, for its response, noting it had participated in previous rescues. These included saving about 100 migrants, including children and pregnant women, in the Strait of Sicily just five days earlier, ship officials said.

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.

On Monday, the Gregoretti brought the 24 bodies to Malta for burial, before continuing to Sicily with 27 of the survivors. One survivor, a 32-year-old Bangladeshi, had been flown Sunday to Catania, his statements giving authorities the first hint of the tragedy's scale.

The remaining survivors were brought Tuesday to a migrant holding center in Catania and were "very tired, very shocked, silent," according to Flavio Di Giacomo of the IOM.

The survivors were all men, including four teenagers; Sami described them as "very confused, fragile and scared."

For most, the ordeal began well before stepping aboard the doomed boat. They included 350 Eritreans, many of them young men fleeing forced conscription, as well as people from war-torn Syria and Somalia, in addition to migrants from Sierra Leone, Mali, Senegal, Gambia, Ivory Coast and Ethiopia.

Prosecutors said Tuesday that some had been held for as long as 30 days on a farm near where the boat was docked before being transported in groups of about 30 in trucks to the embarking point.

"In one instance, one of the migrants was allegedly struck with a club because he stepped away" to go to the bathroom, they said in a statement.

Save the Children said witness statements indicated that 60 children and adolescents were on board the ship, only four of whom survived. It said if current trends continue, 2,500 children could die this year, calling on European leaders to restart rescue operations.

The children surviving the journeys are "exhausted and traumatized not only from the ordeal but also during their long and dangerous land journeys," said Gemma Parkin, a Save the Children spokeswoman in Sicily.

"But they also tell us they are grateful to be alive and in a safe place — they know they are the lucky ones."