Lampedusa, Italy (CNN) -- At the port in Lampedusa, recovery teams continue to fill trucks with the bodies they're still pulling from the sea.
More than 300 so far -- and that number could rise.
They are among the more than 500 African migrants believed to have been aboard a boat that sank off the island last Thursday. The tragedy amounted to Italy's deadliest migrant shipwreck and, according to Lampedusa Mayor Giusi Nicolini, "the biggest sea tragedy in the Mediterranean Sea since World War II."
The survivors -- 155 of them, mainly from Eritrea, who swam for their lives and were lucky enough to be rescued by fishermen and the Coast Guard -- wait in a cramped migrant detention center.
It was built to hold about 250 people but has held many times that in recent days. Each day, more people are leaving on ferries for other detention centers along the Italian coast, though 900 nonetheless remained Tuesday.
The traumatic firsthand accounts are helping build a picture of why the boat ended up on the seabed of the Mediterranean with most of its passengers entombed below deck.
One of them, 30-year-old Germani Nagassi, told CNN he'll never forget what he saw.
"For five hours we were floating, using the dead bodies of our companions," he said. "There is nothing worse than this. There were many children. There was a mother with her four children, a mother with an infant, all lost at sea. My mind is scarred and in a terrible condition."
Perilous journey, then 13 days at sea
The voyage to Lampedusa was supposed to be one of the migrant's last on a long, sometimes painful journey to a new life.
Take a woman named Santa, who asked not to use her family name, for fear of retaliation against her family back home in Eritrea. The single mother of a 4-year-old boy felt she had to escape the coastal east African nation, where she had no money for food or medical care.
It was not done on a whim, especially given smugglers' demands.
"Our relatives and friends sold all that they had -- some little gold jewels, a piece of land or their house -- to sponsor our trip," Santa said.
That trek took her across Africa -- jammed tight in jeeps crossing the Sahara Desert with only a few biscuits and juice to sustain them, packed in garages, occasionally beaten with a plastic water pipe if they talked or raised their eyes, she recalled.
Santa and others' hope was simple: to have a better life. But the boat's sinking first threatened her life, and now that she's in Italian custody, her future.
"It's absurd," she said. "We come here, we work to pay our families back -- if we don't die."
She and others spent 13 days at sea before their boat's engine stopped less than a mile from Lampedusa, Italy's closest island to Africa about halfway between Sicily and Tunisia. It's a common destination for refugees seeking to enter European Union countries, and a common site of shipwrecks.
Fire on board
There's been criticism that more was not done to help, that the Italian coast guard was too slow to respond, that they spent precious time filming footage of the rescue instead of saving more lives.
Hamid Mohammad, 18, swears an Italian vessel spotted them in trouble off the coast, but did nothing.
"The Italian's boat started circling around us. They circled our boat twice, then just went away," he said. "That's when people started to panic."
The boat's captain told the passengers to set fire to clothes and blankets to attract attention.
"He gathered some clothes and bed sheets and lit them. But his container of benzene exploded," Mohammad said.
The fire then spread, and when many of the migrants crowded to one side, the boat capsized, said Italian lawmaker Mario Marazziti, citing survivors' accounts.
"People were screaming as the boat capsized," Mohammed said.
The lucky few
In response to criticism, the coast guard Saturday defended its response time and said its crews were on site 20 minutes after receiving the SOS call.
"The moment we got the emergency call from the fishermen at 7 a.m., we immediately intervened and started coordinating the rescue operations," said coast guard spokesman Filippo Marini.
Abrahalli Amare, 23, was one of the lucky few who were eventually rescued.
"We left our country because of hardship, so that we could live in peace and help our families," Amare said."But we have found this bitter sadness. It was so unexpected, so disturbing. And now we can't think of anything else."
Journalist Livia Borghese and CNN's Greg Botelho contributed to this report.